Method and apparatus for controlling numerically controlled machine tool

ABSTRACT

A method and an apparatus for controlling a numerically controlled machine tool, wherein the heat generation amount and the temperature of a drive unit including a servo amplifier  15   b  and a feed shaft motor  3  are computed by a drive unit heat generation amount computing unit  31  by simulation, and from the computed heat generation amount and the computed temperature, the total heat generation amount of the drive unit, the cutting feed heat generation amount, the cutting load heat generation amount, etc. are computed by a feed heat generation amount computing unit  39 , so that the cutting feed rate override value of the numerically controlled machine tool  1  is computed by a cutting feed rate override computing unit  27  and effectuated by being output to a NC unit. Further, based on the temperature of the drive unit computed by a computing unit  31  or the temperature computed by a temperature data computing unit  47  or the temperature detected by a temperature detection sensor  49 , etc., the proper values of the feed acceleration/deceleration time constants τ r  and τ c  are computed and output as a ratio with respect to the set and stored initial values τ r0  and τ C0  thereby to control the NC commanded rate. The overheating of the feed axis drive unit is prevented while at the same time improving the machining efficiency.

TECHNICAL FIELD

The present invention relates generally to a method and an apparatus forcontrolling a numerically controlled machine tool or, in particular, toa method and an apparatus for controlling a numerically controlledmachine tool wherein the machining operation is performed by numericallycontrolling the feed operation of a plurality of feed axes whilepreventing an alarm which otherwise might be issued due to theoverheating of the drive means of each feed axis, thus making itpossible to carry out the machining operation at as high a speed aspossible to realize an improved machining efficiency. Theabove-described machine tool is not limited to a machine tool used onlyfor cutting or grinding, but includes a punch press machine having afeed axis mechanism with a feed motor and a laser beam machine formachining a work with a high energy laser beam. The present invention iswidely applicable to machine tools including these machines.

PRIOR ART

Consideration will be given to a typical machine tool for performing thecutting or grinding operation. In the case where the machining operationof the machine tool is numerically controlled, as is well known, a feedmotor for each of a plurality of feed axes is controlled, with therotation of the main spindle of the machine tool, in accordance with anumerical control program (NC program) which is input to a numericalcontrol unit (NC unit) in advance, and the relative machining operationbetween the work and the machining tool (hereinafter referred to simplyas the tool) is controlled so that the desired machining operation isperformed on the work based on the machining program.

In this type of numerically controlled machine tool, it is indispensablefor securing the machining precision to accurately control the operationof each feed motor for driving the feed operation along each feed axis.At the same time, it is crucial to prevent overheating of the respectivefeed motors, thereby protecting the machine from breakage ormalfunction, in order to achieve a high efficiency in the machiningoperation.

A basic configuration of a numerically controlled machine tool will beconsidered hereinbelow. Generally, the numerically controlled machine isprovided with a machine tool, a numerical control unit, a machinecontrol unit and an electric power unit. The numerical control unitincludes a program read-interpret unit for reading and interpreting theNC program, an interpreted program storage unit for temporarily storingan interpreted program, a program execution command unit for fetchingthe stored program from the interpreted program storage unit whenevernecessary and issuing execution program data, an interpolation andacceleration/deceleration control unit for computing by interpolationthe travel data of the operation designated by the NC program,distributing the travel data to each feed axis and controlling theacceleration and deceleration of each feed axis, and a servo controlunit for issuing a position command and for correcting the positioncommand and the speed command in accordance with a feedback signal. Theservo control unit, in turn, includes a control unit for outputting amotor command signal and a servo amplifier for amplifying the output ofthe control unit and generating a motor drive current, wherein thecurrent generated by the servo amplifier is used for controlling anddriving each of the feed motors of the machine tool.

Also, the machine body of the machine tool includes a main spindlehaving a tool or the like mounted thereon and rotationally driven by thespindle motor, a spindle head for rotatably supporting the main spindle,a feed motor configured with a servo motor for driving the feedingoperation of each of a plurality of feed axes described above, aposition detector provided for each feed axis to detect the currentposition data with the feeding operation of each feed axis, and aworktable having appropriately mounted thereon a workpiece to bemachined and adapted to travel along a plurality of feed axes withrespect to the base of the machine body. The main spindle motor, eachfeed motor and the position detector are connected to the numericalcontrol unit, the machine control unit and the electric power unitthrough a signal line and a power line. The servo amplifier for thenumerical control unit described above supplies a desired amount ofelectric drive current to each feed motor of the machine body of themachine tool, based on the power introduced from the electric powerunit, and each feed motor is driven so as to set the tool at a desiredmachining position. Also, the tool and the workpiece are movedrelatively along the feed axes so that the machining operation such ascutting or grinding of the workpiece is performed. In the presentinvention, all elements for drive use, including the servo amplifier ofthe servo control unit provided for the numerical control unit and thefeed motor supplied with the electric drive current from the servoamplifier, are collectively called a drive means for a feed axis or feedaxes.

Now, the drive means of a feed axis, which includes a servo amplifierand a feed motor provided for a numerically controlled machine tool, isbasically designed to be capable of exhibiting a sufficient machiningperformance at a rated current value. As long as the machine tool isoperated or driven at or below the rated current value, continuousoperation is possible, but in a case where the rated current isexceeded, a discontinuous operation may be permitted. When the operationexceeding the rated current occur frequently, the heat generation by thefeed motor increases, so that the motor-temperature MT of the feed motorfor the feed axis exceeds a tolerable motor-temperature MTa, determinedto maintain the desired motor performance. In such a case, therefore, analarm signal indicating overheating is generated to stop the operationof the feed motor. FIG. 11, in which the abscissa represents the time Tand the ordinate the motor temperature MT, shows temperature curves forthree cases including (I) the case in which the machine tool is operatedwithout controlling the heat generation amount of the feed motor, (II)the case in which the machine tool is operated by maintaining a ratedheat generation amount determined from the design, and (III) the case inwhich the machine tool is operated while controlling the tolerable heatgeneration amount in accordance with the motor temperature of the feedmotor. In the case (I) where the heat generation amount is notcontrolled, the motor temperature MT quickly exceeds the tolerablemotor-temperature MTa. In the case (II) where the machine tool isoperated to maintain a rated amount of heat generation or in the case(III) where the machine tool is operated to control the tolerable amountof heat generation in accordance with the motor temperature, however, itis found that the operation can be continued without exceeding thetolerable motor-temperature MTa.

The feeding operation performed by each of the feed motors, on the otherhand, includes a machining-feed in which the tool engaging a workpieceis fed to perform the machining operation, and a rapid-feed for quicklyaccomplishing the positioning operation for determining the relativepositions of the tool and the workpiece along each of the feed axes. Therapid-feed is a non-machining operation, and therefore desirablycontributes to the improvement in the machining efficiency by increasingthe speed thereof as far as possible. In fact, the acceleration ordeceleration of the rapid-feed causes an electric current flow three orfour times as large as the rated current in the feed motor. The drivemeans is, however, so configured that unless the electric current valueaveraged for a predetermined elapsed time exceeds the rated currentvalue, the temperature of the feed motor does not increase beyond thetolerable motor-temperature MTa to such a level as to cause anoverheating.

The high-speed machines currently provided are intended to increase thespeed of rotation of the main spindle in order to improve the machiningefficiency and also to increase the speed of the feeding operation.

However, the machining conditions required for the numericallycontrolled machine tool, such as implementing of quick acceleration ordeceleration of the rapid feed and the machining feed, machining ofworkpiece stock lacking good machinability, and acquiring of acomplicated machined contour in a workpiece are so severe that theelectric current supplied for the operation of the feed motors oftenexceeds the rated current during a machining operation with a largemachining load. The result is often that, in both the rapid feed and themachining feed, even the average current value described above exceedsthe rated current value. In other words, the feeding operationaccompanied by a rise and fall in short cycles is repeatedly commanded,with the result that the temporal average current value of the drivemeans exceeds the rated current. Consequently, the drive means includingthe servo amplifier and the feed motor exceeds the tolerabletemperature, with the occasional result that the machine is stopped, byan alarm, to stop the machining operation.

Once the machine tool stops during the machining operations, not onlythe machining efficiency is deteriorated but also a generation ofdefective workpiece occurs, and in the case of unmanned operations, themachine tool is left stationary for a long time before the operation isrestored by the operator. In the prior art, in order to avoid thisinconvenience, the servo amplifier or the servo motor having anunnecessary large capacity has been employed or the numerical controlprogram is produced by the programmer to allow some time margin forreducing the chance of frequent acceleration or deceleration. In otherwords, there still remains a strong demand for the provision of a methodand an apparatus, for performing the feeding operation of thenumerically controlled machine tool, which are capable of obtaining ahigh machining efficiency with the positive intention to increase thespeed of both rapid feed and machining feed and are thus applicable tothe machining operation under severe machining conditions with a largemachining load.

Such being the situation, in the current technical field of numericallycontrolling the operation of a drive means for a numerically controlledmachine tool and an industrial robot, various propositions have beenmade especially to shorten the tact time by optimizing the operation ofthe drive motor providing the drive means on the one hand and to improvethe security of the machine tools and robots as well as the drive motoron the other hand.

Specifically, Japanese Unexamined Patent publication (Kokai) No.6-289917 discloses a method of controlling the feed motor of the machinetool, including a servo motor, intended to improve the machiningprecision and the security of the tools and the machine by reducing thefeeding rate or stopping the machining operation with the increase in aload applied to a feed axis. In the method of controlling the feed motorthe feed motor control system includes a disturbance estimating meansfor estimating the disturbance load torque, which is supplied with acommand torque for the feed motor and an actual speed of the feed motorto compute and estimate the total disturbance torque. An amountequivalent to the friction torque due to dynamic friction is subtractedfrom the estimated total disturbance torque. Thus, the estimateddisturbance torque, i.e. a disturbance load is determined and written ina memory. Then, it is determined at what level the estimated disturbancetorque is located relative to an upper limiting value preset forstopping the machining operation and a lower limiting value forpreventing the deterioration of the machining precision. In this way, anoverride value with respect to the commanded feeding rate is adjusted,and when the lower limiting value is exceeded, the speed of the feedmotor is reduced. If the estimated disturbance torque is reduced belowthe low limiting value as a result, the override value is adjusted againto increase the speed of the feed motor in a feed axis while continuingthe machining operation and to maintain the machining precision. In thecase where the estimated disturbance torque has exceeded the upperlimiting value, on the other hand, the feed motor in the feed axis isstopped to protect the tools and workpiece and the machine from anabnormal load.

In the method of controlling the feed motor by the estimated disturbancetorque disclosed in Japanese Unexamined Patent Publication (Kokai) No.6-289917 described above, a load imposed on the feed motor is estimatedby a special disturbance estimating observer means from the speedcommand value and the feedback value of the actual speed data of thefeed motor, and the estimated value is compared with a preset referencevalue thereby to determine and control the speed of the feed motor. Inthis way, the operating condition of the feed motor is determined onlyfrom the speed, and therefore the operation is not controlled takinginto consideration the thermal factors of the feed motor and the motordrive amplifier constituting the drive means of the machine tool. Theresulting problem is that, especially in the case where a numericallycontrolled machine tool is operated as a high-speed machine for a longtime, the drive means is not necessarily properly controlled. Anotherproblem is the lack of versatility arising from the use of the specialmeans called the disturbance estimating observer means.

On the other hand, a method has been proposed for adequately controllingthe drive motor of the machine by taking a thermal limit intoconsideration, in controlling the operation of the drive motor.

Specifically, Japanese Unexamined Patent publication (Kokai) No. 9-91025discloses method of controlling a drive motor for driving a joint of anindustrial robot about its own axis, in the shortest possible time,taking the thermal limitation into consideration. In the control method,for controlling the drive of the drive motor and controlling the robotoperation for the shortest possible time, a time constant in theacceleration/deceleration of the drive motor is shortened to assure theshortest cycle time, while at the same time monitoring heat generationof the motor during the regenerating operation of the robot to take thethermal limitation of the motor into consideration. Using the result ofthis monitor operation, the time constant in theacceleration/deceleration is adjusted in steps, as required. In thisway, according to this technique, the drive motor of each axis can beoperated within the range of thermal limitation.

In the method of controlling the robot drive motor for the shortestpossible length of time disclosed in Japanese Unexamined Patentpublication (Kokai) No. 0-91025, however, the robot regeneratingoperation is carried out several times by repeating the operatingcycles, from which the thermal limitation, i.e. the tolerable range inan amount of heat generation of the drive motor for each axis isdetermined. Therefore, in an application of this technique to themachine tool, for example, the operating cycle is repeated and the heatgeneration of the drive motor is monitored each time the machiningcondition or the machining load undergoes a change, thereby making itdifficult to accomplish an efficient machining operation.

Further, the machining operation by a numerically controlled machinetool often lasts for a long time, and often has an extremely longoperating cycle as compared with the operating cycle of industrialrobots. Therefore, it is considered inadequate to use the control methodof Japanese Unexamined Patent publication (Kokai) No. 9-91025 describedabove for determining the thermal condition of the drive means for themachining operation of a numerically controlled machine tool.

On the other hand, Japanese Unexamined Patent Publication (Kokai) No.9-179623 of the present applicant has disclosed an invention relating toa method and an apparatus for numerically controlling a machiningapparatus without overheating the drive means even after continuoushigh-speed operation repeating acceleration and deceleration of thedrive means of the feed axes at the time of rapid feed. In thisparticular invention, the temperature of the drive means including amotor drive amplifier and a feed motor for each axis of the drive systemof the machining apparatus is predictively computed according to theelectric current data or the torque command data fed back to atemperature data computing unit from a servo control unit, and thustemperature data is produced. This temperature data is compared with apredetermined temperature data tolerable for the drive means stored in adata storage unit in advance, by an acceleration/deceleration timeconstant computing unit connected to the temperature data computingunit, and in accordance with the result of comparison, theacceleration/deceleration time constant of any particular feed axis ischanged. Thus, in the disclosed method and apparatus for controlling anumerically controlled machining apparatus operable with highefficiency, the thermal conditions of the drive means are taken intoaccount, so that the machining apparatus can be operated continuouslywithout overheating the drive means or reducing the commanded feedingrate. The acceleration/deceleration time constant in this case is aconstant to determine an acceleration when a feeding speed in a feedaxis is changed, and the constant is closely associated with a timerequired for changing the feeding speed in the feed axis.

The aforementioned invention can be regarded to include the technicalmeans for permitting a continuous high-speed operation of the drivemeans without overheating by changing the acceleration/deceleration timeconstant while taking the thermal factors into consideration, and thuscan be considered as being highly advantageous in that when it isapplied to the numerically controlled machine tool an efficientmachining operation can be performed even under severe machiningconditions and heavy machining load, such as machining of a workpieceinto one having a complicated shape, rigid dimensional requirements inmachining of a workpiece, and worse machinability of a workpiece stock.

Nevertheless, the invention relating to a method and an apparatus fornumerically controlling a machining apparatus, provided by the presentapplicant and described above, emphasizes only temperature data of thedrive means and fails to take into consideration a change in the mode ofthe rapid feed of the drive means and the machining feed for themachining operations such as cutting, grinding, laser beam machining andthe punch press or the heat generation amount of the drive means.Therefore, it is desired to provide a method and an apparatus for moreprecisely controlling the drive means in each of the feed axes.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to advance a furtherstep from the aforementioned invention relating to a method and anapparatus for numerically controlling a machining system proposed by thepresent applicant, i.e., to provide a method and an apparatus, forcontrolling a numerically controlled machine tool, in which a rapid feedand a machining feed are driven by the drive means of each of the feedaxes and the machining operation can be continued for long time with ahigh machining efficiency without causing overheating even underrepetitive heavy machining loads.

In view of the above-described object of the present invention, inaccordance with one aspect of the present invention, there is provided amethod of controlling a numerically controlled machine tool byperforming a numerical control program supplied from a read andinterpret unit of a numerical control unit to control a drive means ofat least one feed axis via an execution command unit, an interpolationunit and a servo control unit, comprising the steps of:

presetting acceleration/deceleration time constants for rapid feed andcutting feed of the feed axis, and data on predetermined temperature andheat generation amount tolerable for the drive means of said feed axis;

computing a temperature of said drive means based on control data ofsaid numerical control program;

determining a heat generation amount tolerable for said drive means inaccordance with the computed temperature of said drive means;

computing a total amount of heat generation of said drive mean within apredetermined time, a rapid feed heat generation amount within apredetermined time during a rapid feed operation and a cutting feed heatgeneration amount within a predetermined time during a cutting feedoperation, based on the control data of the numerical control program;

comparing each of the computed total heat generation amount within thepredetermined time, the rapid feed heat generation amount within thepredetermined time and the cutting feed heat generation amount withinthe predetermined time with the afore-determined tolerable heatgeneration amount, respectively; and

controlling an acceleration/deceleration time constant for at least oneof the rapid feed operation and the cutting feed operation of the feedaxis in accordance with the result of comparison.

In accordance with another embodiment of the present invention, there isprovided a method of controlling a numerically controlled machine toolby performing a numerical control program supplied from a read andinterpret unit of a numerical control unit so as to control a drivemeans of at least one feed axis via an execution command unit, aninterpolation unit and a servo control unit, comprising the steps of:

presetting acceleration/deceleration time constants for rapid andcutting feed operations of the feed axis, a cutting feed rate, andpredetermined temperature and heat generation amount data tolerable forsaid drive means of the feed axis;

computing a temperature of said drive means based on the control data insaid numerical control program;

determining an amount of heat generation tolerable for said drive meansin accordance with the computed temperature of said drive means;

computing, during the cutting feed operation, a cutting feed heatgeneration amount and a cutting load heat generation amount in responseto a cutting load, based on control data of the numerical controlprogram;

comparing the determined tolerable heat generation amount with thecomputed cutting feed heat generation amount; and

controlling a cutting feed rate of said feed axis from the result ofsaid comparing step while taking a ratio that the computed amount of thecutting load heat generation represents of the cutting feed heatgeneration amount into consideration.

In accordance with still another embodiment of the present invention,there is provided a method of controlling a numerically controlledmachine tool by performing a numerical control program supplied from aread and interpret unit of a numerical control unit so as to control adrive means of at least one feed axis, via an execution command unit, aninterpolation unit and a servo control unit, comprising the steps of:

presetting acceleration/deceleration time constants τr0 and τC0 duringrapid and cutting feed operations, respectively, of the feed axis, andtemperature data representing a predetermined temperature MT and heatgeneration amount data representing a predetermined heat generationamount Qa which are tolerable for said drive means of the feed axis;

computing the temperature and the heat generation amount at each momentof said drive means from the current data or the torque command dataoutput from said servo control unit to said drive means;

determining the heat generation amount Qa tolerable within apredetermined time t of said drive means in accordance with the computedtemperature at each moment;

computing the total heat generation amount QA within said predeterminedtime t, the rapid feed heat generation amount QR at the time of rapidfeed and the cutting feed heat generation amount QC at the time ofcutting feed of said drive means from the computed heat generationamount at each moment;

comparing the total heat generation amount QA within the computedpredetermined time t with the determined tolerable heat generationamount Qa;

computing the acceleration/deceleration time constants τr and τC forrapid feed and cutting feed, respectively, of said feed axis inaccordance with the ratio which the rapid feed heat generation amount QRand the cutting feed heat generation amount QC represent of said totalheat generation amount QA within the predetermined time t, in the casewhere said total heat generation amount QA within said predeterminedtime t is larger than said tolerable heat generation amount Qa; and

controlling the acceleration/deceleration time constants for rapid feedand cutting feed of said feed axis by changing the set time constantsτr0 and τC0 to the computed time constants τr and τC, respectively.

In accordance with a further embodiment of the present invention, thereis provided a method of controlling a numerically controlled machinetool by performing a numerical control program supplied from a read andinterpret unit of a numerical control unit so as to control a drivemeans of at least one feed axis, via an execution command unit, aninterpolation unit and a servo control unit, comprising the steps of:

presetting acceleration/deceleration time constants of the feed axis, acutting feed rate, predetermined temperature data tolerable for thedrive means of the feed axis and tolerable predetermined heat generationamount data;

predictively computing a temperature at each moment of the drive meansbased on control data of the numerical control program and a heatgeneration amount at each moment;

comparing the computed temperature with the set tolerable predeterminedtemperature data;

controlling acceleration/deceleration time constants of the feed axis inaccordance with the result of comparison while determining a tolerableheat generation amount of the drive means in accordance with thecomputed temperature at each moment;

computing a cutting feed heat generation amount of the drive meansduring a cutting feed operation from the computed heat generation amountat each moment;

computing a cutting load heat generation amount corresponding to acutting load of the drive means based on the control data of thenumerical control program;

comparing the computed cutting feed heat generation amount with thedetermined tolerable heat generation amount; and

controlling a cutting feed rate of the feed axis in accordance with theratio which the computed cutting load heat generation amount representsof the cutting feed heat generation amount from the result ofcomparison.

In accordance with a further embodiment of the present invention, thereis provided a method of controlling a numerically controlled machinetool for executing, through an execution command unit, an interpolationunit and a servo control unit, a numerical control program fetched froma read and interpret unit of a numerical control unit and controlling adrive means of at least one feed axis, comprising the steps of:

presetting curves representing acceleration/deceleration time constantsfor the feed axis, cutting feed rates and tolerable predeterminedtemperatures of the drive means of the feed axis and a curverepresenting predetermined tolerable heat generation amount;

computing temperatures at respective moments of the drive means fromcurrent data or torque command data output from a servo control unit tothe drive means to produce a temperature curve containing the computedtemperatures and to compute heat generation amounts at the respectivemoments;

comparing an inclination of the produced temperature curve with aninclination of the temperature curve representing the set predeterminedtolerable temperatures;

computing acceleration/deceleration time constants of the feed axis froma relation between the inclination of the temperature curve representingthe set tolerable predetermined temperatures and theacceleration/deceleration time constants to control theacceleration/deceleration time constants of the feed axis and todetermine the tolerable heat generation amount of the drive means inaccordance with the computed temperatures at the respective moments,when the inclination of the produced temperature curve is larger thanthat of the temperature curve representing the set tolerablepredetermined temperature;

computing the cutting feed heat generation amount during cutting feedoperation of the drive means from the computed heat generation amount atthe respective moments;

computing a cutting load heat generation amount corresponding to acutting load applied to the drive means from the current data or thetorque command data output from the servo control unit to the drivemeans;

comparing the computed cutting feed heat generation amount with thedetermined tolerable heat generation amount; and

controlling the cutting feed rate of the feed axis in accordance withthe ratio which the computed cutting load heat generation amountrepresents of the cutting feed heat generation amount from the result ofcomparison.

In accordance with a still further embodiment of the present invention,there is provided a method of controlling a numerically controlledmachine tool for executing, through an execution command unit, aninterpolation unit and a servo control unit, a numeral control programfetched from a read and interpret unit of a numerical control unit andcontrolling a drive means of at least one feed axis, comprising thesteps of:

presetting acceleration/deceleration time constants for the feed axis,cutting feed rates, predetermined tolerable temperature data of thedrive means for the feed axis, predetermined tolerable heat generationamount data and tolerable number of times accelerated/decelerated perunit time;

counting number of times accelerated/decelerated per unit of the drivemeans from the program data transferred from the read and interpret unitor the execution command unit of the numerical control unit;

comparing the counted number of times accelerated/decelerated per unittime with the set tolerable number of times accelerated/decelerated perunit time;

computing the acceleration/deceleration constants for the feed axis froma relation between the set number of times accelerated/decelerated perunit time and the acceleration/deceleration time constants to controlthe acceleration/deceleration time constants of the feed axis, and tocompute the cutting load heat generation amount corresponding totemperatures, heat generation amount and cutting load at respectivemoments of the drive means from the current data or the torque commanddata output from the servo control means to the drive means, when thecounted number of times accelerated/decelerated exceeds the tolerablenumber of times accelerated/decelerated;

determining the tolerable heat generation amount of the drive means inaccordance with the computed temperatures at respective moments tocompute a cutting feed heat generation amount during cutting feedoperation of the drive means from the heat generation amounts atrespective moments;

comparing the computed cutting feed heat generation amount with thedetermined tolerable heat generation amount; and

controlling the cutting feed rate of the feed axis in accordance withthe ratio which the computed cut load generation amount represents ofthe cutting feed heat generation amount from the result of comparison.

In accordance with a yet further embodiment of the invention, there isprovided a method of controlling a numerically controlled machine toolfor executing, through an execution command unit, an interpolation unitand a servo control unit, a numeral control program fetched from a readand interpret unit of a numerical control unit and controlling a drivemeans of at least one feed axis, comprising the steps of:

presetting acceleration/deceleration time constants of the feed axis,cutting feed rates, tolerable predetermined temperature data of thedrive means for the feed axis and tolerable predetermined heatgeneration amount data;

detecting a temperature of the drive means;

comparing the detected temperature data with the set tolerablepredetermined temperature data;

adjustably increasing the acceleration/deceleration time constants ofthe feed axis, while computing the heat generation amount at each momentof the drive means and the cutting load heat generation amountcorresponding to a cutting load from the current data or the torquecommand data output from the servo control unit to the drive means, whenthe detected temperature data is higher than the set tolerablepredetermined temperature data;

determining the tolerable heat generation amount of the drive meanscorresponding to the detected temperature;

computing the cutting feed heat generation amount at the time of cuttingfeed of the drive means from the computed heat generation amount at eachmoment;

comparing the computed cutting feed heat generation amount with thedetermined tolerable heat generation amount; and

controlling the cutting feed rate of the feed axis in accordance withthe ratio which the computed cut load heat generation amount representsof the cutting feed heat generation amount from the result ofcomparison.

In accordance with another aspect of the present invention, there isprovided an apparatus for controlling a numerically controlled machinetool for executing, through an execution command unit, an interpolationunit and a servo control unit, a numeral control program fetched from aread and interpret unit of a numerical control unit and controlling adrive means of at least one feed axis, comprising:

data storage means for setting and storing acceleration/decelerationtime constants for rapid feed and cutting feed of the feed axis,tolerable predetermined temperature data of the drive means of the feedaxis and predetermined tolerable heat generation amount data;

temperature computing means for computing a temperature of the drivemeans based on control data of the numerical control program;

tolerable heat generation amount determining means for determining atolerable heat generation amount of the drive means in accordance withthe temperature computed in the temperature computing means;

heat generation amount computing means for computing a total heatgeneration amount of the drive means within a predetermined time, arapid feed heat generation amount at the time of rapid feed and acutting feed heat generation amount at the time of cutting feed based onthe control data of the numerical control program; and

acceleration/deceleration time constant computing means for computingand outputting the acceleration/deceleration time constants for the feedaxis based on the total heat generation amount within a predeterminedtime, the rapid feed heat generation amount and the cutting feed heatgeneration amount computed in said heat generation amount computingmeans and the tolerable heat generation amount determined in thetolerable heat generation amount determining means.

In accordance with another embodiment of the present invention, there isprovided an apparatus for controlling a numerically controlled machinetool for executing, through an execution command unit, an interpolationunit and a servo control unit, the numerical control program fetchedfrom a read and interpret unit of a numerical control unit andcontrolling the drive means of at least one feed axis, comprising:

data storage means for setting and storing cutting feed rate of the feedaxis and tolerable predetermined heat generation amount data of thedrive means of the feed axis;

temperature computing means for computing a temperature of the drivemeans based on a control data of the numerical control program;

tolerable heat generation amount determining means for determining atolerable heat generation amount of the drive means in accordance withthe temperature computed in the temperature computing means;

heat generation amount computing means for computing a heat generationamount of the drive means based on the control data of the numericalcontrol program; and

cutting feed rate computing means for computing a cutting load of thedrive means based on the control data of the numerical control programto compute and deliver a cutting feed rate of the feed axis based on acutting load heat generation amount corresponding to the computedcutting load, a cutting feed heat generation amount computed by the heatgeneration amount computing means and the tolerable heat. generationamount determined by the tolerable heat generation amount determiningmeans.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the left half portion of theconfiguration, divided for simplicity's sake, of a control unit of anumerically controlled machine tool according to a first embodiment ofthe present invention;

FIG. 2 is a block diagram showing the right half portion of theconfiguration, divided for simplicity's sake, of the control unit of thenumerically controlled machine tool according to a first embodiment ofthe present invention;

FIG. 3 is a block diagram showing the left half portion of theconfiguration, divided for simplicity's sake, of a control unit of anumerically controlled machine tool according to a second embodiment ofthe present invention;

FIG. 4 is a block diagram showing the right half portion of theconfiguration, divided for simplicity's sake, of the control unit of thenumerically controlled machine tool according to the second embodimentof the present invention;

FIG. 5 is a block diagram showing the left half portion of theconfiguration, divided for brevity's sake, of a control unit of anumerically controlled machine tool according to a third embodiment ofthe present invention;

FIG. 6 is a block diagram showing the right half portion of theconfiguration, divided for simplicity's sake, of the control unit of thenumerically controlled machine tool according to the third embodiment ofthe present invention;

FIG. 7 is a block diagram showing the left half portion of theconfiguration, divided for brevity's sake, of a control unit of anumerically controlled machine tool according to a fourth embodiment ofthe present invention;

FIG. 8 is a block diagram showing the right half portion of theconfiguration, divided for brevity's sake, of the control unit of thenumerically controlled machine tool according to the fourth embodimentof the present invention;

FIG. 9 is a block diagram showing the left half portion of theconfiguration, divided for brevity's sake, of a control unit of anumerically controlled machine tool according to a fifth embodiment ofthe present invention;

FIG. 10 is a block diagram showing the right half portion of theconfiguration, divided for brevity's sake, of the control unit of anumerically controlled machine tool according to the fifth embodiment ofthe present invention;

FIG. 11 is a graph showing temperature curves as against a motortolerable temperature MTa, in which the abscissa thereof represents thetime T and the ordinate thereof represents the motor temperature MT;

FIG. 12 is a graph showing the total heat generation amount QA of adrive means including a servo amplifier and a feed motor and heatgeneration amounts by the type of feeding including a rapid feed and acutting feed with the respective tolerable heat generation amounts Qa,compared with each other along the ordinate for each predetermined timet of the abscissa representing the time T;

FIG. 13 is a graph showing the acceleration/deceleration time constantsand the cutting feed rate override value with the operation timing alongthe ordinate for each predetermined time t of the abscissa representingthe time T;

FIG. 14 is a graph showing the curve of the tolerable heat generationamount Qa of the drive means changing with time against a rated heatgeneration amount QT corresponding to the rated current, with theabscissa thereof representing the time T and the ordinate thereofrepresenting the tolerable heat generation amount Qa;

FIG. 15 is a graph showing temperature curves of the feed motor or theservo amplifier with respect to the elapsed time T and the change in theinclination θ thereof according to the first to fifth embodiments;

FIG. 16 is a graph showing the relation between the inclination θ of thetemperature curve shown in FIG. 15 and the acceleration/decelerationtime constant τ according to the second to fifth embodiments;

FIG. 17 is a graph showing the relation between the number of timesaccelerated/decelerated per unit time and the acceleration/decelerationtime constant τ according to the fourth/embodiment;

FIG. 18 shows the first half portion of the flowchart representing thecontrol steps of a control method according to the first embodiment;

FIG. 19 shows the last half portion of the same flowchart;

FIG. 20 shows the first half portion of the flowchart representing thecontrol steps of a control method according to the second embodiment;

FIG. 21 shows the last half portion of the same flowchart;

FIG. 22 is a flowchart showing the remaining portion of the controlsteps of a control method according to the second embodiment;

FIG. 23 shows the first half portion of the flowchart representing apart of the control steps of a control method according to the thirdembodiment;

FIG. 24 shows the last half portion of the same flowchart;

FIG. 25 is a flowchart showing the remaining portion of the controlsteps of a control method according to the third embodiment;

FIG. 26 shows the first half portion of the flowchart representing apart of the control steps of a control method according to the fourthembodiment;

FIG. 27 shows the last half portion of the same flowchart;

FIG. 28 is a flowchart showing the remaining portion of the controlsteps of a control method according to the fourth embodiment;

FIG. 29 shows the first half portion of the flowchart representing apart of the control steps of a control method according to the fifthembodiment;

FIG. 30 shows the last half portion of the same flowchart; and,

FIG. 31 is a flowchart showing the remaining portion of the controlsteps of a control method according to the fifth embodiment.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention will be described below, in more detail, based onthe various embodiments shown in the accompanying drawings. Theseembodiments will be explained with reference to the case in which anumerically controlled machine tool performs the cutting operation on awork, and therefore the feed modes of the machine tool are assumed toinclude the rapid feed mode and the cutting feed mode. In the case ofother machines such as the punch press and the laser beam machine forperforming press work and fusing work, respectively, therefore, thepresent invention can be understood to include the two feed modes ofrapid feed and machining feed as described above.

First, by referring to the block diagrams of FIGS. 1 and 2 showing afirst embodiment of the invention, a configuration is shown fornumerically driving and controlling a plurality of feed axes, each beingprovided with a linear feed mechanism or a rotational feed mechanism ofa numerically controlled machine tool 1. In this way, the numericallycontrolled machine tool 1 generally has a plurality of feed axes. One ofthe feed axes, shown as a representative, is driven by a feed motor 3having a feed amount detection means EC including a pulse coder, forexample, for detecting the amount of feed along a feed axis. An NCprogram 5 includes sequentially coded operation commands to be performedby the numerically controlled machine tool 1. The NC program 5 is readand interpreted by a program read and interpret unit 7, and temporarilystored in an interpreted program storage unit 9 forming a buffer unit. Aprogram execution command unit 11 connected to the interpreted programstorage unit 9 receives the program from the interpreted program storageunit 9 and sends out the program data in accordance with the progress ofthe operation of the numerically controlled machine tool 1. The programdata mainly contains the travel commands for each feed axis.

The program data thus sent out is received by the interpolation andacceleration/deceleration control unit 13 for performing theinterpolation computation for travel of each feed axis and theacceleration/deceleration computation according to the speed curve ofacceleration and deceleration of the feed axis before or afterinterpolation. The result of computation is sent out to a servo controlunit 15. This servo control unit 15 includes a position & speed controlunit 15 a and a servo amplifier 15 b for driving the motor. The positionand speed control unit 15 a generates a drive current value or a torquecommand value to be supplied to the feed motor 3, from the positioncommand, the speed command and the acceleration command of each feedaxis and sends the resulting value to the servo amplifier 15 b. Theservo amplifier 15 b, upon receipt of the drive current value or thetorque command value, fetches and generates the current for actuallydriving the feed motor 3 from a power unit not shown, and supplies it tothe feed motor 3. Thus, the numerically controlled machine tool 1performs the machining operation under a desired numerical control bythe sequence of operations beforehand input to the NC program 5.

In the event that this machining operation is accompanied by repetitiveacceleration/deceleration of the feeds between a tool (not shown) heldby a main spindle of the machine tool body and a workpiece to bemachined, i.e. the two feeds including a rapid feed mainly intended forpositioning and a cutting feed mainly intended for machining such ascutting, then the servo amplifier 15 b and the feed motor 3 generateheat. When either of them reaches an upper limit of a tolerabletemperature, a thermal alarm is issued so that the operation of thenumerically controlled machine tool 1 is stopped in an emergency mode.In the configuration described above, the various function units fromthe NC program 5 to the first stage of the servo control unit 15 areassociated with the numerical control unit (hereinafter referred to as aNC unit) including a later-described parameter storage unit 25. Ofcourse, the feed motor 3 is a component element belonging to the body ofthe numerically controlled machine tool 1. The “drive means” describedthroughout the specification of the present invention is intended toinclude the servo amplifier 15 b and the feed motor 3. A firstembodiment constituting a control method and a control apparatus inwhich neither the servo amplifier 15 b nor the feed motor 3 isoverheated will be described in more detail.

First, a data storage unit 17 is provided as a means for storing theconstants and the data required for performing a control methodaccording to the invention. The design parameters and the known data,determined by experiment in advance and stored and set in the datastorage unit 17, include the computation formulae executed and used inthe execution in the drive means heat generation model 33, the drivemeans heat radiation model 35 and the drive means heat accumulationmodel 37 of the drive means heat generation amount computing unit 31described later, the constants in the formulae and the initial valuestherein. Also included are the motor constant associated with theperformance of the feed motor 3, the tolerable temperature and the ratedcurrent value, the rated heat generation amount QT based on the ratedcurrent value of the feed motor 3 and the servo amplifier 15 b, theacceleration/deceleration time constant τ 0 of the feed axis adapted forthe numerically controlled machine tool 1, the relation between thecurrent data or the torque command data produced from the servo controlunit 15 and the temperature of the drive means, the temperature curverepresenting the temperature change of the drive means supplied with therated current continuously, and the relation between the inclination θof the temperature curve and the acceleration/deceleration time constantτ of the feed axis.

The tolerable heat generation amount computing unit 19 computes thetolerable heat generation amount Qa of the drive means based on therated heat generation amount QT due to the data stored and set in thedata storage unit 17 and the temperature output from the drive meansheat accumulation model 37 described later.

The tolerable heat generation amount computing unit 19 is connected tothe rapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21 and the cut feed rate override computing unit 27. Therapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21 computes the acceleration/deceleration time constants(the cutting feed acceleration/deceleration time constant τC and therapid feed acceleration/deceleration time constant τr) for the rapidfeed mode and the cutting feed mode in accordance with the heatgeneration amount data, described later, for the two modes computedbased on the current value or the torque command value produced from theposition/speed control unit 15 a of the servo control unit 15 through afeedback circuit on the one hand and the data of the tolerable heatgeneration amount Qa obtained from the tolerable heat generation amountcomputing unit 19 on the other hand. This process will be furtherdescribed later.

The cutting feed rate override computing unit 27, on the other hand,determines by computation whether or not to use a cutting feed rateoverride value, i.e. the (percent) value obtained by multiplying thecommand value of a predetermined cutting feed rate designated in the NCprogram 5 in advance in design stage by the percentage value of 0through several hundred % (normally, 0 through 100%), as an actualoverride value, based on the tolerable heat generation amount dataobtained from the tolerable heat generation amount computing unit 19,the various heat generation amount data of the drive means obtained fromthe total heat generation amount computing unit 41 of the feed heatgeneration amount computing unit 39 described later and the cutting feedheat generation amount/cutting feed acceleration/deceleration heatgeneration amount computing unit 43, and the machining load dataincluding the cutting load obtained by conversion and computation of thetorque command value produced from the position/speed control unit 15 aof the servo control unit 15 through a feedback circuit. The overridevalue of the cutting feed rate computed by the cutting feed rateoverride computing unit 27 is supplied as a priority feed rate data tothe interpolation and acceleration/deceleration control unit 13 of theNC unit described above through the cutting feed rate override commandunit 29.

The acceleration/deceleration time constants τC and τr for the two modescomputed by the rapid feed/cutting feed acceleration/deceleration timeconstant computing unit 21 are sent to the parameter storage unit 25 ofthe NC unit through the rapid feed/cutting feedacceleration/deceleration time constant command unit 23, and then sentout to the interpolation and acceleration/deceleration control unit 13at an appropriate timing.

The drive means heat generation amount computing unit 31 includes adrive means heat generation model 33 constituting a function unit forperforming the model computation of the heat generation amount of theservo amplifier 15 b and the feed motor 3 constituting the drive meansaccording to a predetermined computation formula, a drive means heatradiation model 35 for performing the model computation of the heatradiation amount corresponding to the ambient temperature environmentand the cooling conditions of the drive means according to apredetermined computation formula, and a drive means heat accumulationmodel 37 for performing the model computation of the heat accumulationamount of the drive means according to a predetermined computationformula. The drive means heat generation model 33 computes the heatgeneration amount of the drive means by introducing the current value orthe torque command value at each moment fetched from the servo controlunit 15 of the NC unit into the computation formula. In this case, thecurrent value or the torque command value are fetched from the servocontrol unit 15 by sampling. The drive means heat accumulation model 37substrates the heat radiation amount computed by the drive means heatradiation model 35 from the heat generation amount of the drive meanscomputed by the drive means heat generation model 33 thereby todetermine the heat accumulation amount of the drive means. The drivemeans accumulates the heat and has a temperature according to this heataccumulation amount, which temperature value is provided by the drivemeans heat accumulation model 37 as an output temperature. Of course,the output temperature is fed back also from the drive means heataccumulation model 37 to the drive means heat radiation model 35 andthus, directly participates in the computation of the heat radiationamount. By the way, in the case of the feed motor 3, for example, thecomputation by the drive means heat generation model 33, the drive meansheat radiation model 35 and the drive means heat accumulation model 37is executed by simulation according to equations (1) to (3) shown below.Specifically,

Motor heat generation amount:

Qm=γI²  (1)

where γ is the heat generation constant, I is the current and the motorheat radiation amount per unit time is given as

Qr=α(Tm−1−Ta)  (2)

where α is the heat radiation constant, Tm the motor temperature and Tathe ambient temperature. The motor temperature is given as

Tm=Tm−1+β(a₁Qm−a₂Qr)  (3)

where β is a constant, a₁ is a constant and a₂ is a constant.

In similar fashion, in the case of the servo amplifier 15 b, the heatgeneration amount due to the current flowing in the electrical elementsmaking up the amplifier 15 b, it may be understood that the heatradiation amount involved in the heat radiation and cooling of theelectrical elements using a fan or a cooling fan and the heataccumulation amount generated from the difference between the twopreceding heat amounts is computed by the models 33, 35, 37 according toa predetermined formula.

The temperature value of the drive means obtained from the drive meansheat accumulation model 37 exhibits a temperature curve as shown in FIG.15 for both the feed motor 3 and the servo amplifier 15 b.

Also, the feed heat generation amount computing unit 39 includes a totalheat generation amount computing unit 41, a cutting feed heat generationamount/cutting feed acceleration/deceleration heat generation amountcomputing unit 43, a rapid feed heat generation amount/rapid feedacceleration/deceleration heat generation amount computing unit 45. Thetotal heat generation amount computing unit 41 is provided as a functionunit for computing the total heat generation amount QA by fetching andaccumulating the heat generation amount of the drive means from thedrive means heat generation model 33 of the drive means heat generationamount computing unit 31 at intervals of a predetermined time t.

The cutting feed heat generation amount/cutting feedacceleration/deceleration heat generation amount computing unit 43 issimilarly provided as a function unit for accumulating and computing theheat generation amount QC of the drive means in the cutting feed modeand the cutting feed acceleration/deceleration heat generation amountQCA constituting the heat generation amount accompanying theacceleration/deceleration operation during the cutting feed at intervalsof a predetermined time t. The cutting feed heat generation amount QC iscomputed as the sum (QC=QCL+QCA+QCF) of the dynamic friction heatgeneration amount QCF generated by the dynamic friction in the casewhere the feed motor 3 rotationally operates mainly as a drive means,the cutting load heat generation amount QCL generated by the drive meansunder a cut load and the cutting feed acceleration/deceleration heatgeneration amount QCA described above generated based on theacceleration/deceleration operation at the time of cutting feed.

The rapid feed heat generation amount/rapid feedacceleration/deceleration heat generation amount computing unit 45 isprovided as a function unit for computing the heat generation amount QRof the drive means in rapid feed mode and the rapid feedacceleration/deceleration heat generation amount QRA providing the heatgeneration amount resulting from the acceleration/deceleration operationduring the rapid feed. The rapid feed heat generation amount QR isaccumulated and computed in similar fashion at intervals of apredetermined time t as the sum (QR=QRA+QRF) of the rapid feedacceleration/deceleration heat generation amount QRA and the heatgeneration amount QRF due to the dynamic friction during the rapid feed.

By the way, in the drive means, the vertical feed axis system requires apredetermined amount of power for holding the main spindle head or thelike element to be fed, for example, at a desired position in thevertical direction against free fall, and based on this component of thepower for holding the gravity along the vertical axis, the drive meansfor the vertical feed shaft system generates heat even when stationary.This heat generation amount QS during the stationary state of the drivemeans is included in the total heat generation amount QA of the drivemeans and is accumulated in the total heat generation amount computingunit 41 at intervals of a predetermined time t. As a result, the totalheat generation amount QA is given as the sum (QA=QR+QC+QS) of the threeheat generation amounts including the rapid feed heat generation amountQR, the cutting feed heat generation amount QC and the stationary stateheat generation amount QS.

The total heat generation amount computing unit 41 is constantlyconnected to the drive means heat generation model 33. The cutting feedheat generation amount/cutting feed acceleration/deceleration heatgeneration amount computing unit 43 and the rapid feed heat generationamount/rapid feed acceleration/deceleration heat generation amountcomputing unit 45, on the other hand, are alternately connected to thedrive means heat generation model 33 by being switched in response tothe rapid feed/cutting feed mode signal obtained from the interpolationand acceleration/deceleration control unit 13 of the NC unit, i.e. thesignal indicating the rapid feed mode or the cutting feed mode of thefeed axis mechanism. In the case where the feed axis mechanism is in theacceleration/deceleration operation, the computing units 43, 45 acquirea signal indicating the acceleration/deceleration from the interpolationand acceleration/deceleration control unit 13 of the NC unit, andperforms the computation of the cutting feed acceleration/decelerationheat generation amount QCA or the rapid feed acceleration/decelerationheat generation amount QRA.

The heat generation amount computed at intervals of a predetermined timet in the total heat generation amount computing unit 41, the cuttingfeed heat generation amount/cutting feed acceleration/deceleration heatgeneration amount computing unit 43 and the rapid feed heat generationamount/rapid feed acceleration/deceleration heat generation amountcomputing unit 45 are shown in relation to the tolerable heat generationamount Qa of the drive means in the graph of FIG. 12. Under thiscondition, in the case where the temperature of the drive means obtainedfrom the drive means heat accumulation model 37 is sufficiently low ascompared with the tolerable temperature, the drive means may be operatedunder the tolerable heat generation amount Qa which is larger than therated heat generation amount QT, as described later. Accordingly, thetolerable heat generation amount Qa is neither predetermined norconstant and assumes various values as shown in FIG. 14.

The rapid feed/cutting feed acceleration/deceleration time constantcomputing 21, in response to the result of computation from theabove-described computing units 41, 43, and 45 of the feed heatgeneration amount computing unit 39, computes and outputs theacceleration/deceleration time constants τr and τC in the feed axisconforming with the state at each moment in the two modes includingrapid feed and cutting feed, based on the relation with the tolerableheat generation amount Qa computed in the tolerable heat generationamount computing unit 19. The graph in the upper part of FIG. 13 showsthe acceleration/deceleration time constants τr and τC at predeterminedintervals of time t, as a variation amount from the initial values τr0and τC0 , respectively, computed and determined by the feed heatgeneration amount computing unit 39 in accordance with the total heatgeneration amount QA, the rapid feed or cutting feed heat generationamount QR or QC, respectively, and the tolerable heat generation amountQa at intervals of a predetermined time t.

The rapid feed/cutting feed acceleration/deceleration time constantcommand unit 23 connected to the rapid feed/cutting feedacceleration/deceleration time constant computing unit 12 temporarilystores, in the parameter storage unit 25, the acceleration/decelerationtime constants τr and τC in the feed axis conforming to the state, ateach moment, of each feed mode output in order to match the timing withthe progress of operation of the numerically controlled machine tool 1,and then gives a command and inputs the acceleration/deceleration timeconstants τr, τC to the interpolation and acceleration/decelerationcontrol unit 13 of the NC unit. The tolerable heat generation amount Qacomputed and supplied by the tolerable heat generation amount computingunit 19, depending on the temperature in the data storage unit 17 or thetemperature output from the drive means heat accumulation model 37, isincreased beyond the rated heat generation amount QT (the heatgeneration amount with the drive means operated at a rated currentvalue) in the stage where the drive means is low in temperature such asin the daily process of starting operation of the machine tool, and withan increase in temperature, the tolerable heat generation amount Qa isbrought nearer to the rated heat generation amount QT based on thetolerable heat generation curve as shown in FIG. 14. The tolerable heatgeneration amount Qa, therefore, is not always set at a constant value.

The total heat generation amount QA computed in the total heatgeneration amount computing unit 41 of the feed heat generation amountcomputing unit 39, the cutting feed heat generation amount QC and thecutting feed acceleration/deceleration heat generation amount QCAcomputed in the cutting feed heat generation amount/cutting feedacceleration/deceleration heat generation amount 43 are sent to thecutting feed rate override computing unit 27. At the same time, thecutting feed rate override computing unit 27 computes the override valueof the cutting feed rate by fetching, together with QA and QC describedabove, the tolerable heat generation amount Qa from the tolerable heatgeneration amount computing unit 19 and the cutting load value from theposition/speed control unit 15 a of the servo control unit 15 describedabove through a feedback circuit. The cut feed rate override valuecomputed by the cut feed rate override computing unit 27 is applied tothe interpolation and acceleration/deceleration control unit 13 of theNC unit through the cut feed rate override common unit 29, so that thecutting feed rate of each feed axis due to the drive means is controlledin accordance with the override value thus computed. The graph in thelower part of FIG. 13 shows the override value FV of the cutting feedrate computed for a predetermined time t described above.

A control method according to the first embodiment having theconfiguration of FIGS. 1 and 2 will be explained hereinbelow withreference to FIGS. 18 and 19. In the flow charts in and subsequent toFIGS. 18 and 19, alphanumeric characters are used as symbols forsimplicity's sake. These characters have the meaning and contentsdescribed above and are listed again for reference.

MT is a motor temperature, MTa is a motor tolerable temperature, T isthe time along the time axis, t is a predetermined time interval foraccumulating and computing the heat generation amount, QA is the totalheat generation amount, QR is the rapid feed heat generation amount, QCis the cutting feed heat generation amount, QS is the stationary stateheat generation amount, QRA is the rapid feed acceleration/decelerationheat generation amount, QRF is the rapid feed dynamic friction heatgeneration amount, QCL is the cutting load heat generation amount QT isthe rated heat generation amount of the drive means, Qa is the tolerableheat generation amount of the drive means, τC is the cutting feedacceleration/deceleration time constant, τr is the rapid feedacceleration/deceleration time constant, and FV is the override value.

First, various required data are stored in the data storage unit 17(step S1). The required data include various constants and the ratedcurrent determined in the design stage, tolerable temperature data,initial values τC0 and τr0 of the acceleration/deceleration timeconstant for the servo amplifier 15 b and the feed motor 3, and thecontents of various equations including (1) through (3) used forcomputation in the drive means heat generation amount computing unit 31.In this setting operation, normally, the above-described design data andthe data determined by experiment in advance are stored and set in themanufacturing and assembling stages of the numerically controlledmachine tool 1. Then, when the numerically controlled machine tool 1 isoperated according to the NC program 5, the current data or the torquecommand data from the servo control unit 15 are sequentially introducedinto the drive means heat generation model 33 (step S2). In this case,the current data or the torque command data are fetched by sampling atvery small intervals of time on the order of 5 ms, for example.

Then, in accordance with the current data or the torque command datathus fetched, the drive means heat generation mode 33, the drive meansheat radiation model 35 and the drive means heat accumulation model 37perform computation by simulation, at each moment, of the servoamplifier 15 b and the feed motor 3 constituting the drive meansaccording to the respective computation formula, and output thetemperature data (the temperature curves (1), (2), etc. in FIG. 15, forexample) of the drive means with the lapse of time from the drive meansheat accumulation model 37 to the drive means heat generation amountcomputing unit 31 (step S3).

Thus, the tolerable heat generation amount computing unit 19 computesthe tolerable heat generation amount Qa corresponding to the temperatureof the feed motor, for example, based on the rated heat generationamount data preset in the data storage unit 17 and the temperature dataof the drive means obtained from the drive means heat generation amountcomputing unit 31 (step S4). In this case, when the motor temperature MTis sufficiently low as compared with the tolerable temperature MTastored in the data storage unit 17, the curve of FIG. 14 is beforehandstored in the data storage unit 17 or the tolerable heat generationamount computing unit 19 in such a manner that the tolerable heatgeneration amount Qa may assume a large value located on the left sideof the curve of FIG. 14.

Upon complete computation of the tolerable heat generation amount Qa,the computation in the feed heat generation amount computing unit 39 isstarted. Specifically, the total heat generation amount QA (=QR+QC+QS)is computed in the total heat generation computing unit 41 at intervalsof a predetermined time t (step S5). In the case where the sampling timein the example mentioned above is 5 msec, for example, the predeterminedtime is selected at about 1 through 3 minutes.

Then, in accordance with the rapid feed mode signal or the cutting feedmode signal transferred from the interpolation andacceleration/deceleration control unit 13, it is determined whether ornot the operation in the feed axis is in rapid feed mode (step S6). Inthe case of rapid feed mode, a process is performed to compute the rapidfeed heat generation amount QR for a predetermined time t (step S7).Unless the rapid mode is prevailing, on the other hand, the processproceeds to the step of determining whether or not the cutting feed modeis prevailing (step S8). In the case of cutting feed mode, the cuttingfeed heat generation amount/cutting feed acceleration/deceleration heatgeneration amount computing unit 43 computes the cutting feed heatgeneration amount QC and the cutting load heat generation amount QCL atintervals of time t (step S9). When it is determined that neither therapid feed mode nor the cutting feed mode is prevailing, it isdetermined that the feeding in the feed axis is stopped and the processproceeds to the next step and waits for the lapse of a predeterminedtime t (step S10).

In this way, in step S10, it is first determined whether or not a presettime t has elapsed as a time interval performing the heat generationamount computation.

In the case where the predetermined time t has not yet elapsed, theprocess returns to the above-described step S2 to restart thecomputation thereby to compute the heat generation amounts QA, QR, QC,QCL for a predetermined time interval t.

The total heat generation amount QA, the rapid feed mode heat generationamount QR and the cutting feed mode heat generation amounts QC, QCLcomputed at intervals of predetermined time t are transferred from thecomputing units 41, 43, 45, respectively, to be sent to the rapidfeed/cutting feed acceleration/deceleration time constant computing unit21 and the cut feed rate override computing unit 27.

In this way, the relative magnitudes of the total heat generation amountQA and the tolerable heat generation amount Qa are determined in therapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21 and the cutting feed rate override computing unit 27(step S11). When the total heat generation amount QA of the drive meansis larger than the tolerable heat generation amount Qa, i.e. when theline of the tolerable heat generation amount Qa is exceeded in the graphin the upper part of FIG. 12, the acceleration/deceleration timeconstants τr and τC are changed and adjusted to make sure that the totalheat generation amount QA becomes less than that tolerable heatgeneration amount Qa. Also, the computation for changing and adjustingthe override FV of the cutting feed rate is performed in the rapidfeed/cutting feed acceleration/deceleration time constant computing unit21 and the cutting feed rate override computing unit 27 (step S12).

The computation in step S12 will be explained more specifically. WhenQA>Qa, the proportion of the excess of QA which represents Qa iscomputed. At the same time, the proper rapid feed and cut feedacceleration/deceleration time constants τr, τC corresponding to theratio which the rapid feed heat generation amount QR and the cuttingfeed heat generation amount, QC represent of the total heat generationamount QA are computed and output by the rapid feed/cutting feedacceleration/deceleration time constant computing unit 21. On the otherhand, based on the cutting load value fetched from the servo controlunit 15, the cutting feed rate override computing unit 27 computes theratio at which the cutting feed rate override value FV is changed to thereference override value FV 0 set according to the cutting feed ratecommand based on the NC program 5 to it output in accordance with theratio which the cut load heat generation amount QCL represents of thecut feed heat generation amount QC.

In the case where it is determined in the process of step S11 that thecondition QA>Qa is not satisfied, on the other hand, the processproceeds to step S13 for determining whether or not the total heatgeneration amount QA is smaller than the tolerable heat generationamount Qa (QA<Qa). If the relation QA<Qa is established as a result, itindicates that the total heat generation amount QA is smaller than thetolerable heat generation amount Qa of the drive means, and thereforethe acceleration/deceleration time constants τr, τC and the overridevalue FV for increasing the total heat generation amount QA or thecutting feed rate to the extent not to exceed the tolerable heatgeneration amount Qa are computed (step S14). More specifically, in stepS14, the acceleration/deceleration time constants τr, τC are computedand transferred in such a manner as to reach a value near the initialvalues τr0 and τC0 thereof, respectively, in accordance with the ratiowhich the rapid feed/cutting feed heat generation amounts QR and QCrepresent of the total heat generation QA. Also, the value of theoverride FV of the cut feed rate is computed and output as a value nearthe reference override value FV 0 initially set (for example, thecommanded rate in the NC program 5 is set to 100% of the initially setoverride value) in accordance with the ratio which the cutting load heatgeneration amount QCL represents of the cut feed heat generation amountQC.

In the case where it is determined in step S13 that the relation QA<Qais not satisfied, on the other hand, it is determined that the totalheat generation amount QA is equal to the tolerable heat generationamount Qa (QA=Qa), and the next process (step S15) is implemented. Inthis case, the rapid feed/cutting feed acceleration/deceleration timeconstant computing unit 21 and the cutting feed rate override computingunit 27 output the initial values τr0 and τC0 as the presetacceleration/deceleration time constants τr and τC in rapid feed orcutting feed mode and at the same time, the initially set referenceoverride value FV 0 (=100%) as the override value FV of the cutting feedrate.

Once the override values of the acceleration/deceleration time constantsand the cutting feed rate are transferred through the process of stepsS12, S14 or S15 in this way, these data are temporarily stored in theparameter storage unit 25 from the rapid feed/cutting feedacceleration/deceleration time constant command unit 23, and output tothe interpolation and acceleration/deceleration control unit 13 of theNC unit at an appropriate timing. Thus, the parameters of theacceleration/deceleration time constants are effectively rewritten (stepS16), and the override value of the cutting feed rate is transferredfrom the cutting feed rate override command unit 29 to the interpolationand acceleration/deceleration control unit 13 as a command value (stepS17).

Upon completion of controlling process after a predetermined time t inthis way, the process is returned to the step S2 to perform the processfor the next predetermined time t, so that the above-described steps ofdetermination and processing are repeated for the new predetermined timet.

The graph of FIG. 13 indicates a change with time of theacceleration/deceleration time constants τr and τC and the overridevalue FV in the two modes of rapid feed and cutting feed after thedetermination step and the processing step repeated for eachpredetermined time t.

As clear from the foregoing description, the control method and theapparatus according to the first embodiment realizes a numericallycontrolled machine tool for machining a workpiece by executing thecommands in accordance with the NC program, in which during theoperation of the feed axis drive means including the servo amplifier 15b and the feed motor 3, the heat generation of the drive means iscomputed by simulation from the numerical control command data therebyto determine the temperature condition, at each moment, of the drivemeans. In addition, the heat generation amount of the drive means iscomputed not only as the total heat generation amount for apredetermined time, but the heat generation amount is computed based ona difference between the rapid feed and cutting feed modes, theacceleration or deceleration or the load change in the machiningoperation. The drive means is controlled not to exceed the tolerabletemperature based on the computed data of the temperature and the heatgeneration amount. Thus, even a machining operation with highacceleration/deceleration frequency or a heavy cutting operation with alarge cutting load can be properly controlled against the tolerable heatgeneration amount while preventing overheating. As a result, the machinetool can be operated for a long time, and the machining efficiency ofthe numerically controlled machine tool can be improved.

The configuration of a second embodiment of the invention will beexplained hereinbelow with reference to FIGS. 3 and 4.

A difference of the second embodiment from the above-described firstembodiment lies in the configuration and the method of computation ofthe acceleration/deceleration time constants for the two modes of rapidfeed and cutting feed. For this reason, the function units having thesame or similar configuration as or to those of the precedingembodiments are designated by the same reference numerals, respectively.

Specifically, according to the second embodiment, the rapid feed/cuttingfeed acceleration/deceleration time constant computing unit 21 has sucha configuration as to receive the temperature data at each moment of thedrive means from the drive means heat generation amount computing unit31. On the other hand, the temperature condition of the drive meansexperimentally determined in advance for each of the feed modes is setand stored as set temperature data in the data storage unit 17, and theset temperature data is input directly from the data storage unit 17 tothe rapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21. Of course, as in the preceding embodiment, the datastorage unit 17 has set and stored therein the various constants ofpredetermined computation formulae for computing the heat generationamount, the heat radiation amount and the heat accumulation amount ofthe drive means, the initial values, the various constants for theperformance of the feed motor and the servo amplifier, the ratedcurrent, the tolerable temperature, etc. together with the settemperature data described above. By the way, in this case, thetolerable temperature of the drive means is set to high when the drivemeans is low in its temperature, and as the temperature increases, setand stored as temperature data nearer to the rated temperature (steadytemperature value for continuous operation at rated current), and thevalues of the acceleration/deceleration time constants τC and τrcorresponding to the temperature data are also set and stored.

A control method according to the second embodiment having theconfiguration of FIGS. 3 and 4 will be explained in detail withreference to the flow chart of FIGS. 20, 21 and 22.

First, the required data are stored in the data storage unit 17 (stepS101). In this case, the required data include the various constants,the rated current and the tolerable temperature curve required fordesigning of the servo amplifier 15 b and the feed motor 3, theacceleration/deceleration time constants τC and τr corresponding to thetolerable temperature curve, the initial values τC0 and τr0 thereof, andthe constants for the various formula including equations (1) through(3) used for the computation in the drive means heat generation amountcomputing unit 31. As in the above-described embodiments, the designingdata and the data experimentally determined in advance are stored andset in the stage of manufacturing and assembling of the numericallycontrolled machine tool 1. Then, when the numerically controlled machinetool 1 is brought into operation according to the NC program 5, thecurrent data or the torque command data are sequentially transferredfrom the servo control unit 15 into the drive means heat generationmodel 33 (step S102). In this case, the current data or the torquecommand data are fetched by sampling for very short times as in thepreceding embodiment.

Then, in accordance with the current data or the torque command datathus fetched, the drive means heat generation model 33, the drive meansheat radiation model 35 and the drive means heat accumulation model 37perform the computation by simulation at each moment according to thecomputation formulae for the servo amplifier 15 b and the feed motor 3making up the drive means. The temperature obtained from the computationresult at each moment is output, as the temperature data of the drivemeans against the lapse of time (the temperature curves (1) and (2) ofFIG. 15, for example), from the drive means heat accumulation model 37in the form of output data of the drive means heat generation amountcomputing means 31 (step S103).

Thus, the tolerable heat generation amount computing unit 19 computesthe tolerable heat generation amount Qa corresponding to the temperatureof the feed shaft motor, for example, based on the data of the ratedheat generation amount set in the data storage unit 17 in advance andthe temperature data of the drive means output from the drive means heatgeneration amount computing unit 31 (step S104).

In the case where the motor temperature MT is sufficiently low ascompared with the tolerable temperature MTa stored in the data storageunit 17, the curve of FIG. 14 is set and stored in the data storage unit17 in such a manner as to increase the tolerable heat generation amountQa to such a large value as to be located on the left side of the curveof FIG. 14.

When the temperature of the drive means computed by simulation in thedrive means heat generation amount computing unit 31 is output from thedrive means heat accumulation model 37, on the other hand, the processof computing the acceleration/deceleration time constants is alsocarried out in accordance with the flow chart of FIG. 22, based on theoutput data of the drive means heat accumulation model 37. This will belater described.

After the computation of the tolerable heat generation amount Qa in stepS104, the computation in the feed heat generation amount computing unit39 is executed. Specifically, the total heat generation amount computingunit 41 computes the total heat generation amount QA (=QR+QC+QS) of thedrive means for each predetermined time t (step S105). By the way, as inthe aforementioned first embodiment, in the case where the sampling timeis 5 msec, for example, the predetermined time t is selected at about 1through 3 min.

Then, in accordance with the rapid feed/cutting feed mode signal outputfrom the interpolation and acceleration/deceleration control unit 13, itis determined whether or not the operation of the feed shaft is in rapidfeed mode (step S106). If the rapid feed mode is involved, the processof computing the rapid feed heat generation amount QR for predeterminedtime t is executed (step S107). In the case where the rapid feed mode isnot involved, on the other hand, the process proceeds to the step fordetermining whether or not the cutting feed mode is prevailing (stepS108). If the cutting feed mode is prevailing, the cutting feed heatgeneration amount QC and the cutting load heat generation amount QCL forthe predetermined time t are computed by the cutting feed heatgeneration amount/cutting feed acceleration/deceleration heat generationamount computing unit 43 (S109). In the case where it is determined thatneither the rapid feed mode nor the cutting feed mode is prevailing, onthe other hand, it is determined that the feeding in feed axis isstopped, and the process proceeds to the next step to wait for the lapseof the predetermined time t (step S110).

In step S110, first, it is determined whether or not a predeterminedtime t has passed as a time interval for executing the computation of aheat generation amount of the drive means.

In the case where the predetermined time t has not yet passed, theprocess returns to step S102 for restarting the computation of thevarious heat generation amounts QA, QR, QC and QCL for the predeterminedtime t.

At this stage, in accordance with the control method of the secondembodiment, the total heat generation amount QA and the cutting feedmode heat generation amounts QC and QCL are transferred from thecomputing units 41 and 43, respectively, to the cutting feed rateoverride computing unit 27.

In this way, the cutting feed rate override computing unit 27 determinesthe relative magnitudes of the total heat generation amount QA and thetolerable heat generation amount Qa (step S111). When the total heatgeneration amount QA is larger than the tolerable heat generation amountQa of the drive means, i.e. when the total heat generation amount QAexceeds a line indicating the tolerable heat generation amount Qa in thegraph in the upper part of FIG. 12, the cutting feed rate overridecomputing unit 27 performs computation in order to change and adjust thecutting feed rate override value FV in such a manner as to reduce thetotal heat generation amount QA below the tolerable heat generationamount Qa (step S112).

A more specific description of the computation in step S112 will beprovided below. When a heat generation amount takes a condition QA>Qa,the ratio which the excess of QA represents of the tolerable heatgeneration amount Qa is computed. At the same time, the cutting feedrate override computing unit 27 computes and outputs, based on the valueof the cutting load fetched from the servo control unit 15, the ratio atwhich the cutting feed rate override value FV is changed with respect tothe reference override value FV 0 determined based on the cutting feedrate command from the NC program 5, in accordance with the ratio whichthe cutting load heat generation amount QCL represents of the cuttingfeed heat generation amount QC.

On the other hand, when it is determined in step S111 that the conditionQA>Qa cannot be met, the process proceeds to step S113 to determinewhether or not the total heat generation amount QA is smaller than thetolerable heat generation amount Qa (QA<Qa). As a result, when thecondition QA<Qa is satisfied, it can be understood that the total heatgeneration amount QA of the drive means is less than the tolerable heatgeneration amount Qa. Therefore, the cutting feed rate override value FVis computed to control the cutting feed rate upward within a range inwhich the total heat generation amount QA does not exceed the tolerableheat generation amount Qa (step S114).

Specifically, in step S114, the value of the override FV near to thereference override value FV 0 (which is set at 100% of the overridevalue set initially for the commanded rate according to the NC program,for example) initially set as the cutting feed rate override value inaccordance with the ratio which the cutting load heat generation amountQCL represents of the cutting feed heat generation amount QC. When it isdetermined in step S113 that the relation QA<Qa is not satisfied, on theother hand, it is determined that the total heat generation amount QA isequal to the tolerable heat generation amount Qa (QA=Qa), and the nextstep (step S115) is performed. Specifically, the cutting feed rateoverride computing unit 27 outputs a reference override value FV 0(=100%) initially set as the cutting feed rate override value FV for thetwo preset modes of rapid feed and cutting feed.

In this way, when the process to output the override value for thecutting feed rate is completed through step S112, S114 or S115, theoverride value FV for the cutting feed rate is transferred from thecutting feed rate override command unit 29 to the interpolation andacceleration/deceleration control unit 13 (Step 116).

With reference to the flow chart of FIG. 22, it is explained that thetemperature of the above-described drive means, for example, thetemperature MT of the feed motor 3 is computed in step S103 and themotor temperature MT indicating the result of computation is transferredas an output from the drive means heat generation amount computing unit31 to the rapid feed/cutting feed acceleration/deceleration timeconstant computing unit 21. Then, the acceleration/deceleration timeconstants τr and τC are computed and output as explained. Similarly, theamplifier temperature of the servo amplifier 15 b is computed and outputby the drive means heat generation amount computing unit 31 from thecurrent data or the torque command data fetched from the servo controlunit 15.

Thus, the temperature data of the drive means is computed from the motortemperature MT and the amplifier temperature (step S118). The rapidfeed/cutting feed acceleration/deceleration time constant computing unit21, on the other hand, reads the temperature data of the drive meanspreset and stored in the data storage unit 17, so that the computedtemperature data is compared with the temperature data preset and stored(step S119).

When it is determined that the computed temperature data is larger thanthe set temperature data (step S120), the rapid feedacceleration/deceleration time constants and the initial values τ 0 andτC0 of the cutting feed acceleration/deceleration time constants set andstored in the data storage unit 17 are adjusted so that the properacceleration/deceleration time constants τr and τC for each of the feedaxes are computed (step S121).

The acceleration/deceleration time constants τr and τC thus computed aretransferred to the rapid feed/cutting feed acceleration time constantcommand unit 23 and, after being temporarily stored in the parameterstorage unit 25, are delivered to the interpolation andacceleration/deceleration control unit 13 of the NC unit in time withthe progress of the operation of the numerically controlled machine tool1 (step S122).

On the other hand, when it is determined in step S120 that the computedtemperature data is smaller than the set temperature data, either theacceleration/deceleration time constants τr0 and τC0 set and stored asdata corresponding to the temperature data preset in the data storageunit 17 or the acceleration/deceleration time constants which arecomputed and adjusted to approach τr0 , τC0 , are output to and storedin the parameter storage unit 25 through the rapid feed/cut feedacceleration/deceleration time constant command unit 23. Subsequently,the stored data are transferred as an output to the interpolation andacceleration/deceleration control unit 13 of the NC unit at anappropriate timing in similar manner (step S123).

In this way, once the acceleration/deceleration time constants τr and τCare transferred as an output to the interpolation andacceleration/deceleration control unit 15 in accordance with thetemperature data of the drive means computed by simulation, theinterpolation and acceleration/deceleration control unit 15, as shown instep S117 of the flow chart of FIG. 20, rewrites the parameters of therapid feed/cutting feed acceleration time constants τr and τC,effectuates them as command data and delivers them to the servo controlunit 15.

Once the control processing for the predetermined time t is completed inthis way, the process returns to step S102 for executing an identicalcontrol processing for the next predetermined time t, so that theabove-described determination and processing are repeatedly performedfor the new predetermined time t.

As described above, in the method and apparatus for controlling thenumerically controlled machine tool according to the second embodiment,the numerically controlled machine tool for machining a workpiece byexecuting the commands in accordance with the NC program computes bysimulation the heat generation of the feed axis drive means includingthe servo amplifier 15 b and the feed motor 3 from the NC command data(the drive current value or the torque command value of the drive means)based on the NC program during the operation of the same feed axis drivemeans. Thus, the temperature data at each moment of the drive means isdetermined. In addition, heat generation amounts due to a change in theoperating mode from the rapid feed to cutting feed and vice versa, to achange in a condition from acceleration to deceleration and vice versa,and to a change in a cutting load are computed, respectively, and thedrive means is controlled not to exceed the tolerable temperature basedon the determined temperature data and the computed data of the heatgeneration amount and the data set and stored in advance as the designvalue or the experimental value. As a result, even in the machiningoperation with frequent sessions of acceleration/deceleration or theheavy cutting operation under a large cutting load, the drive means isadequately controlled with respect to the tolerable heat generationamount, to thereby prevent the drive means from overheating. In thisway, the machine tool can be continuously run for a long time, with theresult that the machining efficiency of the numerically controlledmachine tool is improved, as in the preceding embodiment.

Now, the configuration according to a third embodiment of the inventionwill be explained with reference to FIGS. 5 and 6.

The third embodiment is different from the first and second embodimentsin the configuration and the method for computing theacceleration/deceleration time constants in the two modes of rapid feedand cutting feed. The function units identical or similar to thoseincluded in the configuration of the first and second embodiments,therefore, are designated by the same reference numerals, respectively.

Specifically, the third embodiment is configured in similar manner tothe previous embodiments, in that the current data or the torque commanddata for the feed shaft drive means fetched from the servo control unit15 of the NC unit are input to the drive means heat generation amountcomputing unit 31 so that the temperature data of the drive means arecomputed by simulation. The third embodiment is also similar to theprevious embodiments in that a drive means heat generation model 33 ofthe drive means heat generation amount computing unit 31 is providedwith a feed heat generation amount computing unit 39 for computing theheat generation amount for each of rapid and cutting feed modes and atotal heat generation amount of the drive means, based on the heatgeneration amount computed in accordance with a predeterminedcomputation formula.

Also, the data storage unit 17 has set and stored therein, as atemperature curve, the temperature of the drive means for each of thefeed modes determined experimentally in advance. Further, as in thepreceding embodiment, the data storage unit 17 has stored therein,together with the above-described set temperature curve, the variousconstants and initial values of predetermined computation formulae (1)through (3) for computing the heat generation amount, the heat radiationamount and the heat accumulation amount of the drive means, the variousconstants for the performance of the feed motor 3 and the servoamplifier 15 b, the rated current, and the relation between the currentdata or the torque command data and the temperature of the drive means,the tolerable temperature, etc. The tolerable temperature of the drivemeans is set and stored as data indicating the temperature curve (FIG.15) indicating a temperature change of the drive means supplied with therate current continuously and the relation between the inclination θ ofthe temperature curve and the acceleration/deceleration time constant τof the feed axis. These data are of course determined experimentally inadvance. The temperature curve of the tolerable temperature is set at ahigh level when the drive means is low in temperature in a manner toapproach the rated temperature (the steady temperature value for thecontinuous operation at the rated current) with the increase intemperature. The acceleration/deceleration time constants τC and τrcorresponding to this temperature curve are also set and stored.

Now, the third embodiment, unlike the preceding two embodiments, isprovided with a temperature data computing unit 47. The temperature datacomputing unit 47 acquires the current data and the torque command dataas command data from the servo control unit 15 of the NC unit, andreferring to the relation between the current data or the torque commanddata and the temperature of the drive means obtained from the datastorage unit 17, predictively computes the temperature of the drivemeans at each moment, thereby obtaining the temperature curves (1) and(2) of FIG. 15. Each of the temperature curves computed in thetemperature data computing unit 47 is compared with the temperaturecurve of the tolerable temperature stored in the data storage unit 17 inadvance and, based on the result of comparison, theacceleration/deceleration time constants τC and τr for the two feedmodes of rapid feed and cutting feed are computed in the rapidfeed/cutting feed acceleration/deceleration time constant computing unit21. The result of the computation is transferred to the rapidfeed/cutting feed acceleration/deceleration time constant command unit23 and, further, through the parameter storage unit 25 of the NC unit tothe interpolation and acceleration/deceleration control unit 13. Thecutting feed rate override computing unit 27, on the other hand, is soconnected as to acquire the computation data of the total heatgeneration amount of the drive means from the total heat generationamount computing unit 41 of the feed heat generation amount computingunit 39 on the one hand and the computation data of the cutting feedheat generation amount QC and the cutting load heat generation amountQCL of the drive means from the cutting feed heat generationamount/cutting feed acceleration/deceleration heat generation amountcomputing unit 43 on the other hand. It is also connected to acquire thecommand data on the cutting load value from the servo control unit 15.Further, the cutting feed rate override computing unit 27 is connectedto the tolerable heat generation amount computing unit 19 and soconfigured as to acquire the tolerable heat generation amount Qacomputed by the computing unit 19 based on the rated heat generationamount QT of the drive means fetched from the data storage unit 17 andthe temperature data of the drive means obtained from the drive meansheat generation amount computing unit 31.

In this way, the cutting feed rate override computing unit 27 computes aproper cutting feed rate override value FV from the relation between thetotal heat generation amount QA and the tolerable heat generation amountQa of the drive means in association with the cutting load, and deliversit to the interpolation and acceleration/deceleration control unit 13through the cutting feed rate override command unit 29.

Now, a control method according to the third embodiment will bedescribed in detail with reference to the flow charts shown in FIGS. 23,24 and 25.

First, the required data are stored in the data storage unit 17 (stepS201). The required data include, as described above, the design values,the various data and curves based on experiments and are stored and setin the manufacturing and assembling stage of the numerically controlledmachine tool 1. Then, when the numerically controlled machine tool 1 isoperated on the NC program 5, the current data or the torque commanddata from the servo control unit 15 are sequentially input into thedrive means heat generation model 33 (step S202). In this case, thecurrent data or the torque command data are input by sampling atintervals of a very short time as in the aforementioned embodiments.

In accordance with the current or the torque command data thus fetched,the drive means heat generation model 33, the drive means heat radiationmodel 35 and the drive means heat accumulation model 37 perform thesimulated computation at each moment on the servo amplifier 15 b and thefeed motor 3 making up the drive means, according to the respectivecomputation formulae, and deliver the temperature resulting from thecomputation at each moment in the form of output data of the drive meansheat generation amount computing unit 31 from the drive means heataccumulation model 37 (step S203).

Thus, based on the data of the rated heat generation amount set in thedata storage unit 17 in advance and the temperature data of the drivemeans output from the drive means heat generation amount computing unit31, the tolerable heat generation amount computing unit 19 computes thetolerable heat generation amount Qa corresponding to, for example, thetemperature of the feed shaft motor 3 of the drive means (step S204).

The curve of FIG. 14 is also set and stored in the data storage unit 17so that the tolerable heat generation amount Qa assumes so large a valueas to be located on the left side of the curve of FIG. 14 in the casewhere the motor temperature is sufficient low as compared with thetolerable temperature MTa stored in the data storage unit 17.

On the other hand, when the temperature of the drive means computed bysimulation in the drive means heat generation amount computing unit 31is transferred from the drive means heat accumulation model 37, theprocess for computing the acceleration/deceleration time constant isalso performed according to the flow chart of FIG. 25 based on theoutput data. This will be described later.

Following the computation of the tolerable heat generation amount Qa instep S204, the computation in the feed heat generation amount computingunit 39 is carried out. Specifically, the total heat generation amountcomputing unit 41 computes the total heat generation amount QA(=QR+QC+QS) at intervals of a predetermined time t (step S205). By theway, as in the above-described embodiments, the predetermined time t isselected at a value in the time range of approximately 1 through 3 min.for a sampling time of, say, 5 msec.

Subsequently, it is determined whether or not the operation in the feedaxis is in the rapid feed mode in accordance with the mode signal ofrapid feed or cutting feed output from the interpolation andacceleration/deceleration control unit 13 (step S206). In the case wherethe rapid feed mode is prevailing, the process is executed for computingthe rapid feed heat generation amount QR for a predetermined time t(step S207). Unless the rapid feed mode is involved, in contrast, theprocess proceeds to the step for determining whether or not the cuttingfeed mode is prevailing (step S208). In the case where the cutting feedmode is prevailing, the cutting feed heat generation amount QC and thecutting load heat generation amount QCL for a predetermined time t arecomputed by the cutting feed heat generation amount/cutting feedacceleration/deceleration heat generation amount computing unit 43(S209). Also, in the case where it is determined that neither the rapidfeed mode nor the cutting feed mode is involved, it is determined thatthe feeding operation in the feed axis is stopped, and the processproceeds to the next step to wait until the lapse of the predeterminedtime t (step S210).

In this way, it is determined first in step S210 whether thepredetermined time t set in advance as a time interval for execution ofthe heat generation amount computation has passed or not.

In the case where the predetermined time t has not yet elapsed, theprocess returns to step S202 described above and the computation isrestarted, thereby computing the various heat generation amounts such asQA, QR, QC and QCL for the predetermined time t.

In the process, according to a control method of the third embodiment,the total heat generation amount QA and the cutting feed mode heatgeneration amounts QC and QCL are transferred from the computing units41, 43, respectively, to the cutting feed rate override computing unit27 at intervals of the predetermined time t.

By doing so, the cut feed rate override computing unit 27 determines therelative magnitude of the total heat generation amount QA and thetolerable heat amount Qa (step S211). In the case where the total heatgeneration QA is larger than the tolerable heat generation amount Qa ofthe drive means, i.e. in the state where the total heat generation QAexceeds the line of the tolerable heat generation amount Qa indicated inthe graph in the upper part of FIG. 12, the computation for changing andadjusting the override value FV for the cut feed rate in order to reducethe total heat generation QA to less than the tolerable heat generationamount Qa is executed by the cutting feed rate override computing unit27 (step S212).

More specifically, the computation of step S212 will be explained. Inthe case where QA>Qa, the ratio of the excess of QA with respect to thetolerable heat generation amount Qa is computed. Also, in the cuttingfeed heat rate override computing unit 27, the ratio at which thecutting feed rate override value FV is changed to the reference overridevalue FV 0 determined based on the cutting rate command according to theNC program is computed and delivered in accordance with the ratio whichthe cutting load heat generation amount QCL represents of the cuttingfeed heat generation amount QC based on the cutting load value obtainedfrom the servo control unit 15.

When it is determined in step S211 that the relation QA>Qa cannot besatisfied, on the other hand, the process proceeds to step S213 fordetermining whether or not the total heat generation amount Qa issmaller than the tolerable heat generation amount Qa (QA<Qa). When therelation QA<Qa is established as a result, it indicates that the totalheat generation amount QA of the drive means is less than the tolerableheat generation amount Qa. Therefore, the computation of the cuttingfeed rate override value FV is executed to control the direction inwhich the cutting feed rate is increased within a range of the totalheat generation amount QA not exceeding the tolerable heat generationamount Qa (step S214). More specifically, in step S214, the overridevalue FV (which is set to 100%, for example, of the initially setoverride value in the commanded speed in the NC program 5) of thecutting feed rate near to the initially set reference override value FV0 in accordance with the ratio which the cutting load heat generationamount QCL represents of the cutting feed heat generation amount QC.

When step S213 determines that the relation QA<Qa is not satisfied, onthe other hand, it is determined that the total heat generation amountQA is equal to the tolerable heat generation amount Qa (QA=Qa), and thenext step (step S215) is executed. Specifically, the cutting feed rateoverride computing unit 27 delivers an initially set reference overridevalue FV 0 (=100%) as the cutting feed rate override value FV set inadvance for the two modes of rapid and cutting feeds.

Upon output of the override value of each cutting feed rate through theprocess of steps S212, S214 or S215, the cutting feed rate overridevalue FV is transferred as a command from the cutting feed rate overridecommand unit 29 to the interpolation and acceleration/decelerationcontrol unit 13 (step S216).

By referring to the flow chart shown in FIG. 25, the computation isperformed by the temperature data computing unit 47 to produce atemperature curve of the drive means (step S218). The temperature curvethus produced is output to the rapid feed/cutting feedacceleration/deceleration time constant computing unit 21, whichcompares the inclination θ of the two curves (θ 1 for the temperaturecurve (1) and θ 2 for the temperature curve (2)) with a presettemperature curve (a temperature curve for the rated current, having aninclination θ 0 at the temperature MT 1 on the ordinate of FIG. 15, forexample) sent from the data storage unit 17 (step S219).

When it is determined that the inclination of the temperature curveproduced is larger than the inclination of the set temperature curve, itmeans that the acceleration/deceleration heat generation amounts QRA andQCA for the two feed modes of rapid and cutting feeds are larger thanthe rated heat generation amount QT of the drive means. Therefore, thecomputation is executed for setting the acceleration/deceleration timeconstants τr and τC for each feed axis to a proper value (step S221).

The acceleration/deceleration time constants τr and τC for each feedaxis thus computed are delivered to the interpolation andacceleration/deceleration control unit 13 of the NC unit through theparameter storage unit 25. In other words, the acceleration/decelerationtime constants τr and τC are temporarily stored in the parameter storageunit 25 and are output to the interpolation andacceleration/deceleration control unit 13 at an appropriate timing inkeeping with the progress of operation of the numerically controlledmachine tool 1 (step S222).

When it is determined that the inclination of the temperature curve thusproduced is smaller than the inclination of the set temperature curve,on the other hand, the acceleration/deceleration time constants arecomputed and adjusted to have the initially setacceleration/deceleration time constants τC0 and τr0 or to approach τC0and τr0 , respectively, and are then output to the interpolation andacceleration/deceleration control unit 13 at an appropriate timing inthe same manner as in the preceding case (step S223).

By the way, the temperature curve of the drive means can be in such aform, other than the graph shown in FIG. 15, that the relation betweenthe time T and the inclination θ is expressed as a numerical table atpredetermined time intervals.

Now, an explanation will be provided with regard to the configurationand the operation for a method and an apparatus for controlling thenumerically controlled machine tool according to a fourth embodiment ofthe invention with reference to FIGS. 7 and 8.

The fourth embodiment is a modification of the above-described thirdembodiment. Specifically, the third embodiment takes into considerationthe inclination θ of the temperature curve of the drive means incomputing the acceleration/deceleration time constant for the rapid feedand the cutting feed of the drive means, whereas the fourth embodimenttakes into consideration the number of times the rapid feed or cuttingfeed is accelerated or decelerated.

The normal control process starting from the NC program 5 to the drivecontrol of the feed motor 3 of the numerically controlled machine tool 1is the same in the fourth embodiment as in the first to thirdembodiments described above. Therefore, only the difference inconfiguration will be described below.

First, as in the third embodiment, the fourth embodiment includes thetemperature data computing unit 47. The temperature data computing unit47 of the fourth embodiment, however, is not configured to acquire thecurrent data or the torque command data from the servo control unit 15.Specifically, the temperature data computing unit 47 is connected insuch a manner as to be supplied with the command data from the programread and interpret unit 7 or the program execution command unit 11 ofthe NC unit on the one hand and connected to the data storage unit 17and the rapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21 on the other hand.

The data storage unit 17 has set and stored therein, as determined byexperiments in advance, the initial values of theacceleration/deceleration time constants τr0 and τC0 for rapid feed andcutting feed, respectively, of the feed axis adapted to the numericallycontrolled machine tool 1, the tolerable number of timesaccelerated/decelerated per unit time of the drive means of a feed axisand the relation between the number of times accelerated/decelerated perunit time of the drive means of the feed axis and theacceleration/deceleration time constants τr0 and τC0 of the feed axis asshown in FIG. 17. Also, whenever required, the weight of a workpiece tobe machined, and the sizes of the feed motor 3 and the servo amplifier15 b are also set and stored in the data storage unit 17.

The temperature data computing unit 47, which predictively computes thetemperature data of the feed axis drive means, counts and computes thenumber N of times accelerated/decelerated per unit time as temperaturedata, taking into consideration the number of timesaccelerated/decelerated of the feed axis per unit time correlated withthe temperature of the drive means. In the process, the number N oftimes accelerated/decelerated per unit time is counted by receiving thesame program data as those transferred to the interpolation andacceleration/deceleration control unit 13 from the program executioncommand unit 11 (or the program read and interpret unit 7 as shown bydashed line) in accordance with the progress of the operation.

The rapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21, upon receipt of the result of computation from thetemperature data computing unit 47, computes and outputs theacceleration/deceleration time constants τr and τC of the feed axisadapted to the state at each moment based on the relation between thenumber N of times accelerated/decelerated per unit time and theacceleration/deceleration time constants τr and τC stored in the datastorage unit 17. The rapid feed/cut feed acceleration/deceleration timeconstant command unit 23 issues as a command theacceleration/deceleration time constants τr and τC of the feed axisconforming to the state at each moment output from the rapidfeed/cutting feed acceleration/deceleration time constant computing unit21 to the interpolation and acceleration/deceleration control unit 13through the parameter storage unit 25 of the NC unit in timing with theprogress of operation of the numerically controlled machine tool 1. Ininitial stages of control process, the preset acceleration/decelerationtime constants τr0 and τC0 are directly delivered from the data storageunit 17 to the interpolation and acceleration/deceleration control unit13.

Also in the fourth embodiment comprising the drive means heat generationamount computing unit 31 and the feed heat generation amount computingunit 39, on the other hand, the temperature of the drive means (the feedshaft motor temperature MT, etc.), the rapid feed heat generation amountQR, the rapid feed acceleration/deceleration heat generation amount QRA,the cutting feed heat generation amount QC, the cut feedacceleration/deceleration heat generation amount QCA, the cutting loadheat generation amount QCL, the total heat generation amount QA, etc.are computed and output at each moment based on the current data or thetorque command data of the drive means from the servo control unit 15.Thus, the cutting feed rate override computing unit 27 computes theproper feed rate override value FV for cutting feed of the feed axisfrom the total heat generation amount QA at each moment of the drivemeans as related to the cutting load based on the command data of thecutting load value fetched at each moment from the servo control unit15, the cutting load heat generation amount QCL, and the tolerable heatgeneration amount Qa of the drive means computed by the tolerable heatgeneration amount computing unit 19. The feed rate override value FVthus computed is transferred as a command to the interpolation and theacceleration/deceleration control unit 13 through the cutting feed rateoverride command unit 29. This configuration of giving the cutting feedrate override value FV as a command is exactly the same as that of thefirst to third embodiments described above.

Now, a control method according to the fourth embodiment will bedescribed with reference to the flow charts of FIGS. 26, 27 and 28.

The flow charts of FIGS. 26 and 27 are for explaining the process ofcomputing the override value FV of the cutting feed rate of the drivemeans in the cutting feed rate override computing unit 27 based on thetotal heat generation amount QA, the tolerable heat generation amountQa, the cutting feed heat generation amount QC and the cutting feedacceleration/deceleration heat generation amount QA computed bysimulation of the drive means, taking the total heat generation amountQA and the cutting load heat generation amount QCL as conditions fordetermination, and the process of outputting them to the interpolationand acceleration/deceleration control unit 13 of the NC unit.

These steps S301 through S316, which are identical to steps S201 throughS216 of the above-described third embodiment, are simply a replacementof steps S201 through S216 of the third embodiment and, accordingly,will not be described in detail.

The process of FIG. 28 shown in the flow charts of FIGS. 26 and 27,however, will be described below with reference to the flow chart ofFIG. 28.

FIG. 28 illustrates the process executed by the rapid feed/cutting feedacceleration/deceleration time constant computing unit 21. As describedabove, the temperature data computing unit 47 reads the program datadelivered from the program read and interpret unit 7 or the programexecution command unit 11 of the NC unit (step S318). Then, thetemperature data computing unit 47 counts the number of timesaccelerated/decelerated per unit time of the drive means based on theprogram data thus read (step S319).

Further, the number N of times accelerated/decelerated per unit time aswell as the tolerable number of times accelerated/decelerated per unittime for the drive means set and stored in the data storage unit 17 inadvance are read. Thus, the counted number N of timesaccelerated/decelerated is compared with the tolerable number of timesaccelerated/decelerated (step S320), and it is determined whether or notthe counted number N of times accelerated/decelerated has exceeded thetolerable number of times accelerated/decelerated (step S321). As aresult, when the result of determination shows that the counted number Nof times accelerated/decelerated exceeds the tolerable number of timesaccelerated/decelerated, the proper acceleration/deceleration timeconstants τr and τC adapted to the feed axis at that particular timepoint are computed from the relation shown in FIG. 17 between the numberof times accelerated/decelerated per unit time and the feed axisacceleration/deceleration time constants τr and τC fetched from the datastorage unit 17 (step S322). The computed acceleration/deceleration timeconstants τr and τC are transferred to the interpolation andacceleration/deceleration control unit 13 of the NC unit through therapid feed/cutting feed acceleration/deceleration time constant commandunit 23 and the parameter storage unit 25 (step S323).

When the determination in step S321 indicates that the number N of timesaccelerated/decelerated does not exceed the tolerable number of timesaccelerated/decelerated, it means that the number N of timesaccelerated/decelerated is less than or equal to the tolerable number oftimes accelerated/decelerated. Therefore, the accelerated/decelerationtime constants are computed and adjusted to reach or approach the feedaxis acceleration/deceleration time constants τr0 and τC0 set in stepS301 and transferred to the interpolation and acceleration/decelerationcontrol unit 13 of the NC unit through the rapid feed/cutting feedacceleration/deceleration time constant command unit 23 and theparameter storage unit 25 (step S324). Then, the interpolation andacceleration/deceleration control unit 13 effectuates by rewriting theparameters including the rapid feed/cutting feedacceleration/deceleration time constants τr, τC (step S317 in FIG. 27).

In FIG. 17, the feed axis acceleration/deceleration time constant τr orτC has an upper limit τMAX. It should be understood that this upperlimit value is an acceleration/deceleration time constant at which thedrive means is not overheated even when the acceleration/deceleration iscontinuously repeated, and there exists a maximum number NP of timesaccelerated/decelerated per unit time corresponding to τMAX. Namely, asfar as N is larger than NP, τr and τC becomes τMAX. In the fourthembodiment, taking into account the fact that the temperature of thedrive means and the number of times accelerated/decelerated per unittime are correlated to each other, it is assumed that the process ofcounting the number N of times accelerated/decelerated per unit time astemperature data in the temperature data computing unit 47 is equivalentto the process of computing the temperature data. Of course, thetemperature of the drive means can be predictively computed from thecounted number N of times accelerated/decelerated per unit time and theweight of a workpiece to be machined which is set and stored in the datastorage unit 17 in advance, and the acceleration/deceleration timeconstants for each feed mode of the feed axis can be controlled in amanner similar to the aforementioned embodiments.

The configuration and operation of a method and an apparatus forcontrolling a numerically controlled machine tool according to a fifthembodiment of the present invention will be described below withreference to FIGS. 9 and 10.

The fifth embodiment may be considered as a modification of the thirdembodiment described above. Also, in the fifth embodiment, the normalcontrol operation starting from the NC program 5 to the drive control ofthe feed motor 3 of the numerically controlled machine tool 1 isidentical to the corresponding control operation in the afore-describedfirst through fourth embodiments. Therefore, only the description ofdifferent parts of the configuration will be provided below.

In the afore-described third embodiment, the acceleration/decelerationtime constants τr and τC for rapid feed and cutting feed are computed inthe temperature data computing unit 47 based on the relation between theinclination θ of the temperature curve exhibited by the drive means anda preset inclination of the temperature curve taking the particularinclination θ into account. In accordance with the fifth embodiment, onthe other hand, a temperature detection sensor 49 for measuring thetemperature of the feed motor 3 is further provided (the temperaturemeasurement for the servo amplifier 15 b is effected by the temperaturedetection sensor 49 as shown by dotted line) for computing theacceleration/deceleration time constants for rapid feed and cuttingfeed, so that the actual temperature measurement of the drive means isdelivered to the temperature data computing unit 47 thereby to producethe actual temperature measurement data. Also, theacceleration/deceleration time constants τr and τC for the two modes ofrapid feed and cutting feed are computed in the rapid feed/cutting feedacceleration/deceleration time constant computing unit 21 based on therelation with the tolerable temperature data set and stored in advancein the data storage unit 17, i.e. the data of the tolerable temperatureexperimentally determined in advance by the continuous operation of thedrive means at the rated current, and the acceleration/deceleration timeconstant thus computed is used for the controlling operation.

The data storage unit 17 has set and stored therein, together with theabove-described tolerable temperature data, the experimentallydetermined acceleration/deceleration time constants τr and τC providingthe initial values as related to the tolerable temperature for rapidfeed and cutting feed of the feed axis adapted to the numericallycontrolled machine tool 1. Also, the relation between the detectiontemperature of the temperature detection sensor 49 and the actualtemperature data of the drive means is determined by experiments and setand stored. Further, the size, etc. of the feed motor 3 for each feedaxis and the servo amplifier 15 b are also set and stored.

In the temperature data computing unit 47, the actual temperature of thedrive means (both the feed motor 3 and the servo amplifier 15 b) iscomputed from the temperature data received from the temperaturedetection sensor 49 based on the relation between the detectedtemperature data set and stored in the data storage unit 17 in advanceand the actual temperature. The rapid feed/cutting feedacceleration/deceleration time constant computing unit 21 fetches theactual temperature data of the drive means from the temperature datacomputing unit 47 and the predetermined tolerable temperature of thedrive means from the data storage unit 17, compares the two temperaturesand, in accordance with the result of comparison, computes and outputsthe acceleration/deceleration time constants τr and τC for rapid feedand cutting feed of the feed axis. At the same time, the rapidfeed/cutting feed acceleration/deceleration time constant command unit23 supplies the interpolation acceleration/deceleration control unit 13,through the parameter storage unit 25 of the NC unit, with theacceleration/deceleration time constants τr and τC for rapid feed andcutting feed of the feed axis adapted for each state output from therapid feed/cutting feed acceleration/deceleration time constantcomputing unit 21 as a command, in time with the progress of theoperation of the numerically controlled machine tool 1.

In the initial stages of control, the initial acceleration/decelerationtime constants τr0 and τC0 are directly delivered to the interpolationand acceleration/deceleration control unit 13 from the data storage unit17.

Also in the fifth embodiment, there are provided the drive means heatgeneration amount computing unit 31 and the feed heat generation amountcomputing unit 39, which compute and output at each moment thetemperature of the drive means (feed motor temperature MT), the rapidfeed heat generation amount QR, the rapid feed acceleration/decelerationheat generation amount QRA, the cutting feed heat generation amount QC,the cutting feed acceleration/deceleration heat generation amount QCA,the cutting load heat generation amount QCL and the total heatgeneration amount QA based on the current data or the torque commanddata of the drive means from the servo control unit 15. Therefore, thecutting feed override computing unit 27 computes an adequate feed rateoverride value FV for the cutting feed of the feed axis from the totalheat generation amount QA at each moment of the drive means associatedwith the cutting load, based on the command data of the cutting loadvalue fetched each moment from the servo control unit 15, the cuttingload heat generation amount QCL and the tolerable heat generation amountQa of the drive means which is computed by the tolerable heat generationamount computing unit 19. The feed rate override value FV thus computedis provided as a command output to the interpolation andacceleration/deceleration control unit 13 of the NC unit through thecutting feed rate override command unit 29. This configuration ofproviding a command of the cutting feed rate override value FV isexactly the same as that of the first through fourth embodiments.

Now, a control method according to a fifth embodiment will be explainedwith reference to the flow charts shown in FIGS. 29, 30 and 31.

The flow charts shown in FIGS. 29 and 30 explain the process in whichthe cutting feed rate override value FV is computed by the cutting feedrate override computing unit 27 based on the total heat generationamount QA of the drive means computed by simulation, the tolerable heatgeneration amount Qa, the cutting feed heat generation amount QC and thecutting feed acceleration/deceleration heat generation amount QCA byreference to the total heat generation amount QA and the cutting loadheat generation amount QCL as conditions for determination, and isdelivered as an output to the interpolation andacceleration/deceleration control unit 13 of the NC unit. The process ofsteps S401 through S416, which is identical to that of steps S201through S216 and that of S301 through S316 in the third and fourthembodiments, and can be considered as only a replacement for either oneof the latter two embodiments. Thus, detailed description of the processwill be curtailed below for the sake of brevity. Nevertheless, theprocess of FIG. 31 appearing in the flow chart of FIGS. 29, 30 will beexplained below with reference to the flow chart of FIG. 31.

FIG. 31 illustrates the process executed by the temperature datacomputing unit 47, and as described above, the temperature datacomputing unit 47 receives at each moment the temperature detectionvalue of the drive means from the temperature detection sensor 49 (stepS418) on the one hand, and receives the information of the relationbetween the detected temperature data and the actual temperature of thedrive means based on actual temperature tests from the data storage unit17 on the other hand, so that the temperature data of the drive means iscomputed from these two types of data (step S419).

In the process, the rapid feed/cutting feed acceleration/decelerationtime constant computing unit 21 compares the computed temperature dataof the drive means with the predetermined tolerable temperature data MTaas shown in FIG. 11 fetched from the data storage unit 17 (step S420).Normally, the predetermined tolerable temperature data MTa is set to alevel lower than the upper limit temperature causing an alarm state ofthe drive means according to thermal conditions and slightly higher thanthe shown temperature curve for the rated current.

In the case where the computed temperature data is higher than thetolerable predetermined temperature data MTa (Y in step S421), theacceleration/deceleration time constants τr and τC for the two modes ofrapid feed and cutting feed of the feed axis are reduced by a presetamount into proper acceleration/deceleration time constants (step S422).The result of this computation is delivered to the interpolation andacceleration/deceleration control unit 13 through the rapid feed/cuttingfeed acceleration/deceleration time constant command unit 23 and thedata storage unit 25 of the NC unit (step S423).

When the determination made in step S421 is N, i.e. in the case wherethe computed temperature data is not higher than the predeterminedtolerable temperature data MTa, the acceleration/deceleration timeconstants of the feed axis are computed and adjusted to theacceleration/deceleration time constants τr0 and τC0 or near thereto,and directly sent out to the parameter storage unit 25 temporarilythrough the rapid feed/cutting feed acceleration/deceleration timeconstant command unit 23, and then to the interpolation andacceleration/deceleration control unit 13 (step S424). As a result, asshown in step S417 of FIG. 30, the interpolation andacceleration/deceleration control unit 13 rewrites the parameters of theacceleration/deceleration time constants τr and τC for rapid feed andcutting feed to effectuate them.

The value of the predetermined amount used in the computation forreducing the acceleration/deceleration time constants in step S422 isset and stored in advance in the data storage unit 17 in step S401.

With any of the configurations of the above-described first throughfifth embodiments, the feed axis acceleration/deceleration timeconstants are finally and automatically controlled to adequate values inresponse to the temperature condition of the drive means at each moment.Also, in view of the fact that the cutting feed rate override value isset to a proper value, neither the servo amplifier 15 b nor the feedmotor 3 constituting the drive means causes overheating in any case.

The various embodiments are described above by referring, forconvenience sake, to the case in which the numerically controlledmachine tool performs the cutting operation. It should, however, beunderstood that the present invention is applicable not only to theprocess of cutting a workpiece but also to various numericallycontrolled machines for performing such works as pressing and laser beammachining with equal effect using the drive means including a servoamplifier or the like drive amplifier and a feed motor for driving thefeed axis system. Also, the present invention is not limited to generalmachines but applicable also to robots and other various similarnumerically controlled machines having a linear or rotational feed axissystem and driven by the drive means similar to the one described above.

As will be understood from the foregoing description of the variousembodiments of the present invention, the heat generation and thetemperature of the drive means of a numerically controlled machine toolare computed by simulation by fetching command data based on a NCprogram. Thus, data are obtained at each moment including the total heatgeneration amount of the drive means, the rapid feed/cutting feed heatgeneration amount, the rapid feed/cutting feed acceleration/decelerationheat generation amount and the cutting load heat generation amount, orthe temperature data are determined by computation from the currentvalue or torque command value. Using these various data, theacceleration/deceleration time constants for the two feeds of rapid feedand cutting feed of the machine tool are computed and adjusted toadequate values. At the same time, the override value of the feed rateis computed to a value of a proper ratio with respect to the overridevalue given as an instruction in the NC program in advance andeffectuated by being fed back to the NC Control system. Thus, the drivemeans can be prevented from being overheated without changing thecommanded feed rate based on the NC program.

In view of the fact that the feed rate override value is controlled inaccordance with the heat generation amount of the cutting load, thedrive means can continuously run while avoiding an overheated conditioneven in a machining process performed under a large cutting load. Thus,the machining efficiency of the machining operation under a largecutting load can be appreciably improved as compared with theconventional controlling method.

Further, in the process of computing the temperature of the drive meansby simulation, the tolerable heat generation amount is made variable inaccordance with the temperature of the drive means. When the feed motoris cool at low temperatures, for example, the tolerable heat generationamount is increased to allow the heat generation of the drive means toincrease or, otherwise, the control operation is performed withversatility. Thus, the machining efficiency is further improved.

In addition, since the drive means is controlled automatically to avoidthe overheated condition positively in advance, various burdens appliedto an operator can be considerably reduced as compared with the priorart in which an operator must participate in the operation of anumerically controlled machine tool in order to take into considerationthe machining conditions for preventing overheating.

What is claimed is:
 1. A method of controlling a numerically controlledmachine tool by performing a numerical control program supplied from aread and interpret unit of a numerical control unit to control a drivemeans of at least one feed axis via an execution command unit, aninterpolation unit and a servo control unit, comprising the steps of:presetting acceleration/deceleration time constants for rapid feed andcutting feed of the feed axis, and data on a predetermined temperatureand data on a predetermined heat generation amount tolerable for saiddrive means of said feed axis; computing a temperature of said drivemeans based on control data of said numerical control program;determining a heat generation amount tolerable for said drive means inaccordance with the computed temperature of said drive means; computinga total amount of heat generation of said drive means within apredetermined time, a rapid feed heat generation amount within apredetermined during a rapid feed operation and a cutting feed heatgeneration amount within a predetermined time during a cutting feedoperation, based on the control data of said numerical control program;comparing each of said computed total heat generation amount within thepredetermined time, the rapid feed heat generation amount within thepredetermined time and the cutting feed heat generation within thepredetermined time with the fore-determined tolerable heat generationamount, respectively; and controlling an acceleration/deceleration timeconstant for at least one of the rapid feed operation and the cuttingfeed operation of said feed axis in accordance with a result of saidcomparing step.
 2. A method of controlling a numerically controlledmachine tool by executing a numerical control program fetched from aread and interpret unit of a numerical control unit to control a drivemeans of at least one feed shaft via an execution command unit, aninterpolation unit and a servo control unit, comprising the steps of:presetting acceleration/deceleration time constants for rapid andcutting feed operations of said feed axis, a cutting feed rate, andpredetermined temperature and heat generation amount data tolerable forsaid drive means of said feed axis; computing a temperature of saiddrive means based on control data of said numerical control program;determining an amount of heat generation tolerable for said drive meansin accordance with the computed temperature of said drive means;computing, during the cutting feed operation, a cut feed heat generationamount and a cutting load heat generation amount in response to acutting load, based on control data of said numerical control program;comparing said predetermined tolerable heat generation amount with saidcomputed cutting feed heat generation amount; and controlling a cuttingfeed rate of said feed axis from the result of said comparing step whiletaking a ratio that said computed amount of the cutting load heatgeneration represents of said cutting feed heat generation amount intoconsideration.
 3. A method of controlling a numerically controlledmachine tool by performing a numerical control program fetched from aread and interpret unit of a numerical control unit to control a drivemeans of at least one feed axis via an execution command unit, aninterpolation unit and a servo control unit, comprising the steps of:presetting acceleration/deceleration time constants τr0 and τC0 duringrapid and cutting feed operations, respectively, of said feed axis, andtemperature data representing a predetermined temperature MT and heatgeneration amount data representing a predetermined heat generationamount Qa which are tolerable for said drive means of said feed axis;computing the temperature and the heat generation amount at each momentof said drive means from the current data or the torque command dataoutput from said servo control unit to said drive means; determining theheat generation amount Qa tolerable within a predetermined time t ofsaid drive means in accordance with said computed temperature at eachmoment; computing the total heat generation amount QA within saidpredetermined time t, the rapid feed heat generation amount QR at thetime of rapid feed and the cutting feed heat generation amount QC at thetime of cutting feed of said drive means from said computed heatgeneration amount at each moment; comparing said computed total heatgeneration amount QA within the predetermined time t with saiddetermined tolerable heat generation amount Qa; computing theacceleration/deceleration time constants τr and τC for rapid feed andcutting feed, respectively, of said feed axis in accordance with theratio which said rapid feed heat generation amount QR and said cuttingfeed heat generation amount QC represents of said total heat generationamount QA within said predetermined time t, in the case where the totalheat generation amount QA within said predetermined time t is largerthan said tolerable heat generation amount Qa; and controlling theacceleration/deceleration time constants for rapid feed and cutting feedof said feed axis by changing the set time constants τr0 and τC0 to saidcomputed acceleration/deceleration time constants τr and τC,respectively.
 4. The method of controlling a numerically controlledmachine tool according to claim 3, further comprising the steps of:computing a rapid feed acceleration/deceleration heat generation amountQRA at the time of rapid feed acceleration/deceleration and a cuttingfeed acceleration/deceleration heat generation amount QCA at the time ofcutting feed acceleration/deceleration of said drive means within saidpredetermined time t from said computed heat generation amount at eachmoment; comparing said rapid feed heat generation amount QR and said cutfeed heat generation amount QC within said computed predetermined time twith said determined tolerable heat generation amount Qa; computing saidacceleration/deceleration time constants τr and τC for rapid feed andcutting feed of said feed axis in accordance with a ratio between saidrapid feed acceleration/deceleration heat generation amount QRA and saidcutting feed acceleration/deceleration heat generation amount QCA in thecase where one of said rapid feed heat generation amount QR and saidcutting feed heat generation amount QC within said predetermined time tis larger than said tolerable heat generation amount Qa; and adjustablychanging said acceleration/deceleration time constants for the rapid andcutting feed operations of said feed axis from said setacceleration/deceleration time constants τr0 and τC0 to said computedacceleration/deceleration time constants τr and τC.
 5. The method ofcontrolling a numerically controlled machine tool according to claim 3,further comprising the steps of: setting a cutting feed rate FV 0 ofsaid feed axis; computing a cutting load heat generation amount QCLcorresponding to a cut load applied to said drive means from currentdata or torque command data transferred from said servo control unit tosaid drive means; comparing said computed total heat generation amountQA within said predetermined time t and said cutting feed heatgeneration amount QC with said determined tolerable heat generationamount Qa, respectively; computing a cutting feed rate FV of said feedaxis in accordance with a ratio which said computed cutting load heatgeneration amount QCL represents of said cutting feed heat generationamount QC, in the case where said total heat generation amount QA withinsaid predetermined time t and said cutting feed heat generation amountQC are larger than said tolerable heat generation amount Qa; andadjustably changing said cutting feed rate of said feed axis from saidset cutting feed rate FV 0 to said computed cutting feed rate FV.
 6. Themethod of controlling a numerically controlled machine tool according toclaim 5, further comprising the steps of: comparing said computed totalheat generation amount QA within said predetermined time t with saiddetermined tolerable heat generation amount Qa; controlling saidacceleration/deceleration time constants τr and τC for the rapid andcutting feed operations of said feed axis to approach said setacceleration/deceleration time constants τr0 and τC0 in accordance withthe ratio which said rapid feed heat generation amount QR and saidcutting feed heat generation amount QC represent of said total heatgeneration amount QA with said predetermined time t, in the case wheresaid total heat generation amount QA within said predetermined time t issmaller than said tolerable heat generation amount Qa; comparing saidcomputed total heat generation amount QA within said predetermined timet and said cutting feed heat generation amount QC with said determinedtolerable heat generation amount Qa, respectively; and controlling saidcutting feed rate FV of said feed axis to approach said set cutting feedrate FV 0 in accordance with the ratio which said computed cutting loadheat generation amount QCL represents of said cutting feed heatgeneration amount QC, in the case where said total heat generationamount QA within said predetermined time t and said cut feed heatgeneration amount QC are smaller than said tolerable heat generationamount Qa, respectively.
 7. A method of controlling a numericallycontrolled machine tool by performing a numerical control programfetched from a read and interpret unit of a numerical control unit tocontrol a drive means of at least one feed axis via an execution commandunit, an interpolation unit and a servo control unit, comprising thesteps of: presetting acceleration/deceleration time constants for saidfeed axis, a cut feed rate, data on a predetermined tolerabletemperature of said drive means of said feed axis and data on atolerable predetermined heat generation amount; predictively computingtemperatures of said drive means at respective moments based on controldata of said numerical control program while at the same time computingheat generation amounts at the respective moments; comparing saidcomputed temperatures with said set predetermined tolerable temperaturedata; controlling acceleration/deceleration time constants of said feedaxis in accordance with a result of the comparing step while determininga tolerable heat generation amount of said drive means in accordancewith said computed temperatures of said drive means at respectivemoments; computing a cutting feed heat generation amount during thecutting feed operation of said drive means from said computed heatgeneration amount at each moment; computing a cutting load heatgeneration amount corresponding to a cutting load of said drive means,based on the control data of said numerical control program; comparingsaid computed cutting feed heat generation amounts with said determinedtolerable heat generation amounts; and controlling said cutting feedrate of said feed axis in accordance with the ratio which said computedcutting load heat generation amount represents of said cutting feed heatgeneration amount from the result of the comparing step.
 8. A method ofcontrolling a numerically controlled machine tool by performing anumerical control program fetched from a read and interpret unit of anumerical control unit to control a drive means of at least one feedaxis via an execution command unit, an interpolation unit and a servocontrol unit, comprising the steps of: presettingacceleration/deceleration time constants of said feed axis, a cut feedrate, a curve indicating a predetermined tolerable temperature of saiddrive means of said feed axis and a curve indicating a tolerablepredetermined heat generation amount; computing temperatures atrespective moments of said drive means from current data or torquecommand data transferred from said servo control unit to said drivemeans to produce a temperature curve thereof and to compute a heatgeneration amount at the respective moments; comparing an inclination ofsaid produced temperature curve with that of the temperature curveindicating said set tolerable predetermined temperature; computingacceleration/deceleration time constants of said feed axis from arelation between the inclination of the temperature curve indicatingsaid set tolerable predetermined temperature and saidacceleration/deceleration time constants to control saidacceleration/deceleration time constants of said feed axis and todetermine a tolerable heat generation amount of said drive means inaccordance with said computed temperatures at the respective moments, inthe case where the inclination of said produced temperature curve islarger than that of the temperature curve indicating said set tolerablepredetermined temperature; computing a cutting feed heat generationamount at the time of cutting feed of said drive means from saidcomputed heat generation amount at the respective moments; computing acutting load heat generation amount corresponding to a cutting load ofsaid drive means from the current data or the torque command data outputfrom said servo control unit to said drive means; comparing saidcomputed cutting feed heat generation amount with said determinedtolerable heat generation amount; and controlling the cutting feed rateof said feed axis in accordance with the ratio which said computedcutting load heat generation amount represents of said cutting feed heatgeneration amount from the result of the afore-comparing step.
 9. Amethod of controlling a numerically controlled machine tool by executingthe numerical control program fetched from a read and interpret unit ofa numerical control unit to control a drive means of at least one feedaxis via an execution command unit, an interpolation unit and a servocontrol unit, comprising the steps of: presettingacceleration/deceleration time constants of said feed axis, a cut feedrate, data on a tolerable predetermined temperature of said drive meansof said feed axis, data on a tolerable predetermined heat generationamount and tolerable number of times accelerated/decelerated per unittime; counting the number of times accelerated/decelerated per unit timeof said drive means from a program data output from the read andinterpret unit or said execution command unit of said numerical controlunit; comparing the counted number of times accelerated/decelerated perunit time with said set tolerable number of timesaccelerated/decelerated per unit time; computing theacceleration/deceleration time constants of said feed axis from arelation between the set number of times accelerated/decelerated perunit time and the acceleration/deceleration time constants to controlsaid acceleration/deceleration time constants of said feed axis and tocompute the cutting load heat generation amount corresponding to thetemperature, the heat generation amount and the cutting load atrespective moments of said drive means from the current data or thetorque command data transferred from said servo control unit to saiddrive means, in the case where said counted number of timesaccelerated/decelerated exceeds said tolerable number of timesaccelerated/decelerated; determining said tolerable heat generationamount of said drive means in accordance with said computed temperatureat the respective moments; computing a cutting feed heat generationamount during the cutting feed operation of said drive means from saidcomputed heat generation amount at the respective moments; comparingsaid computed cutting feed heat generation amount with said determinedtolerable heat generation amount; and controlling said cutting feed rateof said feed axis in accordance with the ratio which said computedcutting load heat generation amount represents of said cutting feed heatgeneration amount from the result of the afore-comparing step.
 10. Amethod of controlling a numerically controlled machine tool by executingthe numerical control program fetched from a read and interpret unit ofa numerical control unit to control a drive means of at least one feedaxis via an execution command unit, an interpolation unit and a servocontrol unit, comprising the steps of: presettingacceleration/deceleration time constants of said feed axis, a cut feedrate, data on a predetermined tolerable temperature of said drive meansof said feed axis and data on a predetermined tolerable heat generationamount; detecting temperatures of said drive means; comparing saiddetected temperature data with said set tolerable predeterminedtemperature data; increasing acceleration/deceleration time constants ofsaid feed axis while computing a cutting load heat generation amountcorresponding to a heat generation amount and said cutting load atrespective moments of said drive means from current data or torquecommand data transferred from said servo control unit to said drivemeans, in the case where said detected temperature data is higher thansaid set tolerable predetermined temperature data; determining atolerable heat generation amount of said drive means in accordance withsaid detected temperatures; computing a cut feed heat generation amountduring the cutting feed operation of said drive means from said computedheat generation amount at the respective moments; comparing saidcomputed cutting feed heat generation amount with said determinedtolerable heat generation amount; and controlling the cutting feed rateof said feed axis in accordance with the ratio which said computedcutting load heat generation amount represents of said cutting feed heatgeneration amount from the result of the afore-comparing step.
 11. Anapparatus for controlling a numerically controlled machine tool byexecuting the numerical control program fetched from a read andinterpret unit of a numerical control unit to control a drive means ofat least one feed axis via an execution command unit, an interpolationunit and a servo control unit, comprising: data storage means forsetting and storing acceleration/deceleration time constants for rapidand cut feed operations of the feed axis, data on a tolerablepredetermined temperature of said drive means of said feed axis and dataon a predetermined tolerable heat generation amount; temperaturecomputing means for computing a temperature of said drive means based ona control data of said numerical control program; tolerable heatgeneration amount determining means for determining the tolerable heatgeneration amount of said drive means in accordance with the temperaturecomputed by said temperature computing means; heat generation amountcomputing means for computing a total heat generation amount within apredetermined time, a rapid feed heat generation amount during the rapidfeed operation of said drive means and a cutting feed heat generationamount during the cutting feed operation of said drive means based on acontrol data of said numerical control program; andacceleration/deceleration time constant computing means for computingand outputting said acceleration/deceleration time constant of said feedaxis based on the total heat generation amount within a predeterminedtime computed by said heat generation computing means, the rapid feedheat generation amount, the cutting feed heat generation amount and thetolerable heat generation amount determined by said tolerable heatgeneration amount determining means.
 12. The apparatus for controlling anumerically controlled machine tool according to claim 11: wherein saiddata storage means further sets and stores a cut feed rate of said feedaxis; and wherein said apparatus further comprises a cutting feed ratecomputing means for computing a cutting load of said drive means basedon the control data of said numerical control program, and computing andoutputting the cutting feed rate of said feed axis based on the cuttingload heat generation amount corresponding to said cutting load, thecutting feed heat generation amount computed by said heat generationamount computing means and the tolerable heat generation amountdetermined by said tolerable heat generation amount determining means.13. The apparatus for controlling a numerically controlled machine toolaccording to claim 11, wherein said tolerable predetermined temperaturedata of said feed axis and said tolerable predetermined heat generationamount data set and stored in said data storage means are data on arated temperature and a rated heat generation amount when said drivemeans of said feed axis is operated at a rated current.
 14. Theapparatus for controlling a numerically controlled machine toolaccording to claim 11, wherein said tolerable predetermined temperaturedata and the tolerable predetermined heat generation amount data of saiddrive means of said feed axis set and stored in said data storage meanscomprise a predetermined tolerable temperature data higher than atemperature of said temperature curve in a low temperature area of saidtemperature curve of the temperature data when said drive means of saidfeed axis at a rated current on one hand and predetermined tolerableheat generation amount data larger than said rated heat generationamount in said low temperature area and converged to the rated heatgeneration amount when said drive means of said feed axis is operated atthe rated current according as said low temperature area transfers to ahigh temperature area.
 15. An apparatus for controlling a numericallycontrolled machine tool by executing the numerical control programfetched from a read and interpret unit of a numerical control unit tocontrol a drive means of at least one feed axis via an execution commandunit, an interpolation unit and a servo control unit, comprising: datastorage means for setting and storing a cutting feed rate of said feedaxis, tolerable predetermined temperature data of said drive means ofsaid feed axis, and tolerable predetermined heat generation amount data;temperature computing means for computing a temperature of said drivemeans based on a control data of said numerical control program;tolerable heat generation amount determining means for determining atolerable heat generation amount of said drive means in accordance withthe temperatures computed by said temperature computing means; heatgeneration amount computing means for computing a heat generation amountof said drive means based on the control data of said numerical controlprogram; and cutting feed rate computing means for computing a cuttingload of said drive means based on the control data of said numericalcontrol program while computing and outputting the cutting feed rate ofsaid feed axis based on the cutting load heat generation amountcorresponding to said cutting load, the cutting feed heat generationamount computed by said heat generation amount computing means and thetolerable heat generation amount determined by said tolerable heatgeneration amount determining means.
 16. The apparatus for controlling anumerically controlled machine tool according to claim 15, wherein saiddata storage means further sets and stores acceleration/decelerationtime constants of said feed axis; and wherein said apparatus furthercomprises: acceleration/deceleration time constant computing means forcomputing and outputting the acceleration/deceleration time constants ofsaid feed axis based on the temperatures computed by said temperaturecomputing means and the tolerable predetermined temperature data set insaid data storage means.
 17. The apparatus for controlling a numericallycontrolled machine tool according to claim 15, wherein said data storagemeans further sets and stores a curve indicatingacceleration/deceleration time constants of said feed axis and tolerablepredetermined temperature of said drive means of said feed axis, andwherein said temperature computing means computes temperatures of saiddrive means based on a control data of said numerical control programand produces a temperature curve thereof; said apparatus furthercomprising acceleration/deceleration time constant computing means forcomputing and outputting acceleration/deceleration time constants ofsaid feed axis based on an inclination of the temperature curve producedby said temperature computing means and an inclination of a temperaturecurve indicating tolerable predetermined temperatures set in said datastorage means.
 18. The apparatus for controlling a numericallycontrolled machine tool according to claim 15, wherein said data storagemeans further sets and stores acceleration/deceleration time constantsof said feed axis and tolerable number of times accelerated/deceleratedper unit time of said drive means of said feed axis; and wherein saidapparatus further comprises: acceleration/deceleration time constantcomputing means for computing and outputting acceleration/decelerationtime constants of said feed axis based on number of timesaccelerated/decelerated per unit time as counted from the program dataoutput from the read and interpret unit or the execution command unit ofsaid numerical control unit and the tolerable number of timesaccelerated/decelerated per unit time set in said data storage means.19. The apparatus for controlling a numerically controlled machine toolaccording to claim 15, wherein said data storage means further sets andstores acceleration/deceleration time constants of said feed axis; andwherein said apparatus further comprises: temperature detecting meansfor detecting temperatures of said drive means of said feed axis andacceleration/deceleration time constant computing means for computingand outputting acceleration/deceleration time constants of said feedaxis based on the temperatures detected by said temperature detectingmeans and the tolerable predetermined temperature data set in said datastorage means.
 20. A numerically controlled machining apparatus byexecuting the numerical control program fetched from a read andinterpret unit of a numerical control unit to control a drive means ofeach feed axis via an execution command unit, an interpolation unit anda servo control unit, comprising: a plurality of feed axes, eachincluding a drive means provided with a servo amplifier and a feedmotor; a mechanical assembly including at least a mechanical element anda moving member coupled to each of said feed axes; and a control unitfor controlling the operation of said mechanical assembly; wherein saidcontrol unit comprises: data storage means for setting and storingacceleration/deceleration time constants for rapid and cutting feedoperations of each of said feed axes, a cut feed rate, predeterminedtolerable temperature data of each of said drive means and tolerablepredetermined heat generation amount data; temperature computing meansfor computing by simulation temperatures of said drive means based onthe control data of said numerical control program; tolerable heatgeneration determining means for determining a tolerable heat generationamount of said drive means in accordance with the temperature computedby said temperature computing means; heat generation amount computingmeans for computing a total heat generation amount within apredetermined time of said drive means, a rapid feed heat generationamount at the time of rapid feed, a rapid feed acceleration/decelerationheat generation amount at the time of acceleration/deceleration, acutting feed heat generation amount at the time of cutting feed and acutting feed acceleration/deceleration heat generation amount at thetime of acceleration/deceleration from control data of said numericalcontrol unit; acceleration/deceleration time constant computing meansfor computing and outputting the acceleration/deceleration timeconstants of said feed axes based on the total heat generation amountwithin a predetermined time, the rapid feed heat generation amount, therapid feed acceleration/deceleration heat generation amount and the cutfeed heat generation amount computed by said heat generation amountcomputing means, and the tolerable heat generation amount determined bysaid tolerable heat generation determining means; and cutting feed ratecomputing means for computing a cutting load of each of said drive meansbased on control data of said numerical control program, and computingand outputting a cutting feed rate of each of said feed axes based onthe cutting load heat generation amount corresponding to said cuttingload, the cutting feed heat generation amount computed by said heatgeneration amount computing means and the tolerable heat generationamount determined by said tolerable heat generation determining means.